title: XCode 7.3 crashes when editing XIB
body: <p>I have an XCode project that compiles and runs fine but when I add an element to the UI of a particular XIB it crashes XCode when I try to save or when XCode loses focus. Looking at the error data of the crash it seems to be an Assertion Failure relating to an NSTableHeader but I don't understand where to go from there? I am not using auto-layout and this is an OSX app.</p>
  
  <pre><code>Process:               Xcode [2505]
  Path:                  /Applications/Xcode.app/Contents/MacOS/Xcode
  Identifier:            com.apple.dt.Xcode
  Version:               7.3.1 (10188.1)
  Build Info:            IDEFrameworks-10188001000000000~3
  App Item ID:           497799835
  App External ID:       817226719
  Code Type:             X86-64 (Native)
  Parent Process:        ??? [1]
  Responsible:           Xcode [2505]
  User ID:               501
  
  Date/Time:             2016-06-14 11:30:04.824 -0700
  OS Version:            Mac OS X 10.11.5 (15F34)
  Report Version:        11
  Anonymous UUID:        20048F22-546D-D351-6F8C-D73FF28F4650
  
  
  Time Awake Since Boot: 67000 seconds
  
  System Integrity Protection: enabled
  
  Crashed Thread:        0  Dispatch queue: com.apple.main-thread
  
  Exception Type:        EXC_CRASH (SIGABRT)
  Exception Codes:       0x0000000000000000, 0x0000000000000000
  Exception Note:        EXC_CORPSE_NOTIFY
  
  Application Specific Information:
  ProductBuildVersion: 7D1014
  ASSERTION FAILURE in /Library/Caches/com.apple.xbs/Sources/IDEInterfaceBuilder/IDEInterfaceBuilder-10117/InterfaceBuilderKit/Document/ObjectContainer/IBObjectContainer.m:513
  Details:  Can't get the OID of an object not in the document: &lt;NSTableHeaderView: 0x7fc5daeefd90&gt;
  Object:   &lt;IBObjectContainer: 0x7fc5dae4eeb0&gt;
  Method:   -objectIDForObject:
  Thread:   &lt;NSThread: 0x7fc5d3e17e80&gt;{number = 1, name = main}
  Hints:   None
  Backtrace:
    0   -[IDEAssertionHandler handleFailureInMethod:object:fileName:lineNumber:assertionSignature:messageFormat:arguments:] (in IDEKit)
    1   _DVTAssertionHandler (in DVTFoundation)
    2   _DVTAssertionFailureHandler (in DVTFoundation)
    3   -[IBObjectContainer objectIDForObject:] (in IDEInterfaceBuilderKit)
    4   -[IBDocument objectIDForObject:] (in IDEInterfaceBuilderKit)
    5   -[IBDocument documentArchiver:referenceIDForObject:referenceType:] (in IDEInterfaceBuilderKit)
    6   -[IBDocumentArchiver referenceIDForObject:withReferenceType:] (in IDEInterfaceBuilderKit)
    7   -[IBDocumentArchiver archiveObjectReference:referenceType:forKey:] (in IDEInterfaceBuilderKit)
    8   -[IBDocumentArchiver archiveObjectReference:referenceType:forKey:defaultValue:] (in IDEInterfaceBuilderKit)
    9   -[NSTableView(IBDocumentArchivingGenerator) archiveWithDocumentArchiver:] (in IDEInterfaceBuilderCocoaIntegration)
   10   __51-[IBDocumentArchiver archiveObject:forOptionalKey:]_block_invoke (in IDEInterfaceBuilderKit)
   11   -[IBDocumentArchiver recurseWithElementNamed:forObject:kind:invokingBlock:] (in IDEInterfaceBuilderKit)
   12   -[IBDocumentArchiver archiveObject:forOptionalKey:] (in IDEInterfaceBuilderKit)
   13   __59-[IBDocumentArchiver archiveArray:withName:forOptionalKey:]_block_invoke (in IDEInterfaceBuilderKit)
   14   -[IBDocumentArchiver recurseWithElementNamed:forObject:kind:invokingBlock:] (in IDEInterfaceBuilderKit)
   15   -[IBDocumentArchiver archiveArray:withName:forOptionalKey:] (in IDEInterfaceBuilderKit)
   16   -[IBDocumentArchiver archiveArray:withName:forOptionalKey:defaultValue:] (in IDEInterfaceBuilderKit)
   17   -[NSView(IBViewIntegration) ibArchiveSubviews:] (in IDEInterfaceBuilderKit)
   18   -[NSView(IBDocumentArchivingGenerator) archiveWithDocumentArchiver:] (in IDEInterfaceBuilderKit)
   19   -[IBNSCustomView(IBDocumentArchivingGenerator) archiveWithDocumentArchiver:] (in IDEInterfaceBuilderCocoaIntegration)
   20   __51-[IBDocumentArchiver archiveObject:forOptionalKey:]_block_invoke (in IDEInterfaceBuilderKit)
   21   -[IBDocumentArchiver recurseWithElementNamed:forObject:kind:invokingBlock:] (in IDEInterfaceBuilderKit)
   22   -[IBDocumentArchiver archiveObject:forOptionalKey:] (in IDEInterfaceBuilderKit)
   23   __59-[IBDocumentArchiver archiveArray:withName:forOptionalKey:]_block_invoke (in IDEInterfaceBuilderKit)
   24   -[IBDocumentArchiver recurseWithElementNamed:forObject:kind:invokingBlock:] (in IDEInterfaceBuilderKit)
   25   -[IBDocumentArchiver archiveArray:withName:forOptionalKey:] (in IDEInterfaceBuilderKit)
   26   -[IBDocument archiveTopLevelObjects:] (in IDEInterfaceBuilderKit)
   27   -[IBDocument archiveAndVerifyArchivingOfTopLevelObjects:] (in IDEInterfaceBuilderKit)
   28   -[IBDocument archivePlatformIndependentDataWithDocumentArchiver:] (in IDEInterfaceBuilderKit)
   29   -[IBDocument archiveDocument:] (in IDEInterfaceBuilderKit)
   30   -[IBDocumentArchiver recurseWithElementNamed:forObject:kind:invokingBlock:] (in IDEInterfaceBuilderKit)
   31   -[IBDocumentArchiver archiveDocument:withType:compatibilityVersion:] (in IDEInterfaceBuilderKit)
   32   -[IBDocumentArchiver dataFromArchiveDocument:withType:compatibilityVersion:] (in IDEInterfaceBuilderKit)
   33   __46-[IBDocument fileWrapperOfType:options:error:]_block_invoke (in IDEInterfaceBuilderKit)
   34   -[IBDocument fileWrapperOfType:options:error:] (in IDEInterfaceBuilderKit)
   35   -[IBDocument fileWrapperOfType:error:] (in IDEInterfaceBuilderKit)
   36   -[NSDocument writeToURL:ofType:error:] (in AppKit)
   37   -[IBDocument writeToURL:ofType:error:] (in IDEInterfaceBuilderKit)
   38   -[NSDocument writeToURL:ofType:forSaveOperation:originalContentsURL:error:] (in AppKit)
   39   -[IBDocument writeToURL:ofType:forSaveOperation:originalContentsURL:error:] (in IDEInterfaceBuilderKit)
   40   -[NSDocument _writeSafelyToURL:ofType:forSaveOperation:forceTemporaryDirectory:error:] (in AppKit)
   41   -[NSDocument _writeSafelyToURL:ofType:forSaveOperation:error:] (in AppKit)
   42   -[NSDocument writeSafelyToURL:ofType:forSaveOperation:error:] (in AppKit)
   43   -[IDEEditorDocument writeSafelyToURL:ofType:forSaveOperation:error:] (in IDEKit)
   44   __66-[NSDocument saveToURL:ofType:forSaveOperation:completionHandler:]_block_invoke_22463 (in AppKit)
   45   __66-[NSDocument saveToURL:ofType:forSaveOperation:completionHandler:]_block_invoke2460 (in AppKit)
   46   __66-[NSDocument saveToURL:ofType:forSaveOperation:completionHandler:]_block_invoke_22313 (in AppKit)
   47   __50-[IDEEditorDocument continueFileAccessUsingBlock:]_block_invoke.74 (in IDEKit)
   48   -[NSDocument continueFileAccessUsingBlock:] (in AppKit)
   49   -[IDEEditorDocument continueFileAccessUsingBlock:] (in IDEKit)
   50   __101-[NSDocument _fileCoordinator:asynchronouslyCoordinateReadingContentsAndWritingItemAtURL:byAccessor:]_block_invoke_2 (in AppKit)
   51   __68-[IDEEditorDocument continueAsynchronousWorkOnMainThreadUsingBlock:]_block_invoke (in IDEKit)
   52   __62-[NSDocumentController(NSInternal) _onMainThreadInvokeWorker:]_block_invoke2079 (in AppKit)
   53   __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ (in CoreFoundation)
   54   __CFRunLoopDoBlocks (in CoreFoundation)
   55   __CFRunLoopRun (in CoreFoundation)
   56   CFRunLoopRunSpecific (in CoreFoundation)
   57   RunCurrentEventLoopInMode (in HIToolbox)
   58   ReceiveNextEventCommon (in HIToolbox)
   59   _BlockUntilNextEventMatchingListInModeWithFilter (in HIToolbox)
   60   _DPSNextEvent (in AppKit)
   61   -[NSApplication _nextEventMatchingEventMask:untilDate:inMode:dequeue:] (in AppKit)
   62   -[DVTApplication nextEventMatchingMask:untilDate:inMode:dequeue:] (in DVTKit)
   63   -[NSApplication run] (in AppKit)
   64   NSApplicationMain (in AppKit)
   65  0x000000010c51a39b (in Xcode)
   66   start (in libdyld.dylib)
  
  abort() called
  </code></pre>