title: UIScrollView crashes if setContentOffset is called with animation
body: <p>My application creates instances of a custom subclass of UIView and adds those instances placed horizontally adjacent to each other. When a new instance of my UIView class is created, I can add it to the UIScrollView and reset the contentsize. I then call 
  <code>[UIScrollView setContentOffset:(some point) animated:NO]</code>. 
  This works just fine.
  The issue is when I call the above mentioned method with animation, i.e. 
  <code>[UIScrollView setContentOffset:(some point) animated:YES]</code>
  , the application crashes. 
  The call stack looks like this:</p>
  
  <pre><code>&gt; #0    0x3145b870 in ___forwarding___ ()
  &gt; #1    0x313b6650 in _CF_forwarding_prep_0 ()
  &gt; #2    0x317d84a2 in -[UIAnimator stopAnimation:] ()
  &gt; #3    0x317d84a2 in -[UIAnimator stopAnimation:] ()
  &gt; #4    0x317d7f0e in -[UIAnimator(Static) _advance:withTimestamp:] ()
  &gt; #5    0x317d7e00 in -[UIAnimator(Static) _LCDHeartbeatCallback:] ()
  &gt; #6    0x3531d86e in CA::Display::DisplayLink::dispatch(unsigned long long, unsigned long long) ()
  &gt; #7    0x3531d7c4 in CA::Display::IOMFBDisplayLink::callback(__IOMobileFramebuffer*,
  &gt; unsigned long long, unsigned long long, unsigned long long, void*) ()
  &gt; #8    0x33a56000 in IOMobileFramebufferVsyncNotifyFunc ()
  &gt; #9    0x36e3c60c in IODispatchCalloutFromCFMessage ()
  &gt; #10   0x31422f12 in __CFMachPortPerform ()
  &gt; #11   0x3142d522 in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ ()
  &gt; #12   0x3142d4c4 in __CFRunLoopDoSource1 ()
  &gt; #13   0x3142c312 in __CFRunLoopRun ()
  &gt; #14   0x313af4a4 in CFRunLoopRunSpecific ()
  &gt; #15   0x313af36c in CFRunLoopRunInMode ()
  &gt; #16   0x32888438 in GSEventRunModal ()
  &gt; #17   0x316b4cd4 in UIApplicationMain ()
  </code></pre>
  
  <p>When I enable Zombies, the application output produces:</p>
  
  <pre><code>*** -[__NSArrayM removeObject:]: message sent to deallocated instance 0x113dbb10
  </code></pre>
  
  <p>Additional Info: UIScrollView's delegate is never set. I am using ARC.</p>