title: iOS crash 'NSInternalInconsistencyException', reason: 'statement is still active' Core Data cache related?
body: <p>Very occasionally seeing these pop up in crash reports on screens using <code>NSFetchedResultsController</code>, and not sure how to address them. I don't believe I'm using threading anywhere, unless <code>NSFetchedResults</code> is using them internally.</p>
  
  <p><strong>'NSInternalInconsistencyException', reason: 'statement is still active'</strong> is the full explanation I get.</p>
  
  <p>Two recent stack traces:</p>
  
  <pre><code>0   CoreFoundation                      0x37a368bf __exceptionPreprocess + 163
  1   libobjc.A.dylib                     0x3151c1e5 objc_exception_throw + 33
  2   CoreData                            0x340b2ea5 -[NSSQLiteStatement cachedSQLiteStatement] + 1
  3   CoreData                            0x340b274f -[NSSQLiteConnection prepareSQLStatement:] + 55
  4   CoreData                            0x34156049 -[NSSQLChannel selectRowsWithCachedStatement:] + 61
  5   CoreData                            0x34181d63 newFetchedRowsForFetchPlan_MT + 783
  6   CoreData                            0x340bab07 -[NSSQLCore newRowsForFetchPlan:] + 351
  7   CoreData                            0x34160011 -[NSSQLCore fetchRowForObjectID:] + 1005
  8   CoreData                            0x340cca57 -[NSSQLCore newValuesForObjectWithID:withContext:error:] + 195
  9   CoreData                            0x340cbf83 _PFFaultHandlerLookupRow + 423
  10  CoreData                            0x340cba97 _PF_FulfillDeferredFault + 187
  11  CoreData                            0x340cb94f _sharedIMPL_pvfk_core + 39
  12  PowerPro                            0x0006a779 -[GuestCard getPrimaryProspectiveTenant] (GuestCard.m:77)
  13  PowerPro                            0x00017bf9 -[OutstandingFollowupsViewController configureCell:atIndexPath:] (OutstandingFollowupsViewController.m:208)
  14  PowerPro                            0x00017b9b -[OutstandingFollowupsViewController tableView:cellForRowAtIndexPath:] (OutstandingFollowupsViewController.m:203)
  
  Last Exception Backtrace:
  0   CoreFoundation                      0x37a368bf __exceptionPreprocess + 163
  1   libobjc.A.dylib                     0x3151c1e5 objc_exception_throw + 33
  2   CoreData                            0x340b2ea5 -[NSSQLiteStatement cachedSQLiteStatement] + 1
  3   CoreData                            0x340b274f -[NSSQLiteConnection prepareSQLStatement:] + 55
  4   CoreData                            0x34156049 -[NSSQLChannel selectRowsWithCachedStatement:] + 61
  5   CoreData                            0x340c26eb -[NSSQLCore _newRowsForFetchPlan:selectedBy:withArgument:] + 515
  6   CoreData                            0x340bab3f -[NSSQLCore newRowsForFetchPlan:] + 407
  7   CoreData                            0x3415ea55 -[NSSQLCore newFetchedPKsForSourceID:andRelationship:] + 2217
  8   CoreData                            0x3416a935 -[NSSQLCore newValueForRelationship:forObjectWithID:withContext:error:] + 689
  9   CoreData                            0x34108f8b -[NSFaultHandler retainedFulfillAggregateFaultForObject:andRelationship:withContext:] + 479
  10  CoreData                            0x340dcb23 -[_NSFaultingMutableSet willRead] + 219
  11  CoreData                            0x340dc70b -[_NSFaultingMutableSet count] + 23
  12  PowerPro                            0x00016eb1 -[BrowseGuestCardsViewController configureCell:atIndexPath:] (BrowseGuestCardsViewController.m:246)
  13  PowerPro                            0x00017173 -[BrowseGuestCardsViewController tableView:cellForRowAtIndexPath:] (BrowseGuestCardsViewController.m:222)
  14  UIKit                               0x34e4e9cb -[UITableView(UITableViewInternal) _createPreparedCellForGlobalRow:withIndexPath:] + 547
  15  UIKit                               0x34e4daa9 -[UITableView(_UITableViewPrivate) _updateVisibleCellsNow:] + 1077
  16  UIKit                               0x34e4d233 -[UITableView layoutSubviews] + 207
  17  UIKit                               0x34df1d4b -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 183
  18  CoreFoundation                      0x3799522b -[NSObject performSelector:withObject:] + 43
  19  QuartzCore                          0x3318c381 -[CALayer layoutSublayers] + 217
  20  QuartzCore                          0x3318bf99 CA::Layer::layout_if_needed(CA::Transaction*) + 217
  21  QuartzCore                          0x3318bea5 -[CALayer layoutIfNeeded] + 153
  22  UIKit                               0x34eb6fe1 -[UIButton titleLabel] + 73
  23  PowerPro                            0x00017983 -[BrowseGuestCardsViewController viewDidLoad] (BrowseGuestCardsViewController.m:75)
  </code></pre>