Guard Malloc Crash with UICollectionView

Question

On iOS 7, I have two viewControllers that my app switches between using a Navigation Controller. The 2nd VC contains a UICollectionView and I've subclassed UICollectionViewCell.

When I turn OFF Guard Malloc my app successfully executes the following scenario:

1. Display VC1, where I define some variable number of cells that will populate the UICollectionView in VC2
2. Display VC2, including display of the number of custom UICollectionViewCells I defined in VC1
3. Display VC1, make no change to the number of cells
4. Display VC2, including the same number of custom cells that were displayed in step 2.

When I turn Guard Malloc ON, my app crashes in the middle of step 4. Here's the stack trace:

2013-11-23 18:32:29.568 SongSketchbookTemp2[55597:70b] >>> Entering -[TPXMixViewController collectionView:layout:sizeForItemAtIndexPath:] >>>
2013-11-23 18:32:29.569 SongSketchbookTemp2[55597:70b] <<< Leaving -[TPXMixViewController collectionView:layout:sizeForItemAtIndexPath:] <<<
2013-11-23 18:32:29.570 SongSketchbookTemp2[55597:70b] >>> Entering -[TPXMixViewController collectionView:layout:sizeForItemAtIndexPath:] >>>
2013-11-23 18:32:29.570 SongSketchbookTemp2[55597:70b] <<< Leaving -[TPXMixViewController collectionView:layout:sizeForItemAtIndexPath:] <<<
2013-11-23 18:32:29.571 SongSketchbookTemp2[55597:70b] >>> Entering -[TPXMixViewController collectionView:layout:sizeForItemAtIndexPath:] >>>
2013-11-23 18:32:29.572 SongSketchbookTemp2[55597:70b] <<< Leaving -[TPXMixViewController collectionView:layout:sizeForItemAtIndexPath:] <<<
2013-11-23 18:32:29.573 SongSketchbookTemp2[55597:70b] >>> Entering -[TPXMixViewController collectionView:layout:insetForSectionAtIndex:] >>>
2013-11-23 18:32:29.574 SongSketchbookTemp2[55597:70b] <<< Leaving -[TPXMixViewController collectionView:layout:insetForSectionAtIndex:] <<<
2013-11-23 18:32:29.578 SongSketchbookTemp2[55597:70b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSPlaceholderDictionary initWithCapacity:]: capacity (1184366560) is ridiculous'
*** First throw call stack:
(
    0   CoreFoundation                      0x025fba14 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x023798b6 objc_exception_throw + 44
    2   CoreFoundation                      0x025d32be -[__NSPlaceholderDictionary initWithCapacity:] + 286
    3   UIKit                               0x014a82d5 -[UICollectionView _updateVisibleCellsNow:] + 2123
    4   UIKit                               0x014acb5f -[UICollectionView layoutSubviews] + 265
    5   UIKit                               0x00eec367 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 355
    6   libobjc.A.dylib                     0x0238b81f -[NSObject performSelector:withObject:] + 70
    7   QuartzCore                          0x0021a23a -[CALayer layoutSublayers] + 148
    8   QuartzCore                          0x0020e024 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 380
    9   QuartzCore                          0x0020de90 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 26
    10  QuartzCore                          0x001754a2 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 294
    11  QuartzCore                          0x0017682d _ZN2CA11Transaction6commitEv + 393
    12  QuartzCore                          0x00233390 +[CATransaction flush] + 52
    13  UIKit                               0x00e7d46b _UIApplicationHandleEventQueue + 12967
    14  CoreFoundation                      0x02584cdf __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
    15  CoreFoundation                      0x0258466b __CFRunLoopDoSources0 + 235
    16  CoreFoundation                      0x025a173e __CFRunLoopRun + 910
    17  CoreFoundation                      0x025a0f63 CFRunLoopRunSpecific + 467
    18  CoreFoundation                      0x025a0d7b CFRunLoopRunInMode + 123
    19  GraphicsServices                    0x03b4f2c2 GSEventRunModal + 192
    20  GraphicsServices                    0x03b4f0e9 GSEventRun + 104
    21  UIKit                               0x00e7faab UIApplicationMain + 1225
    22  SongSketchbookTemp2                 0x00002e0d main + 141
    23  libdyld.dylib                       0x037eb70d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

In the run above I defined 3 cells to be displayed. The three calls to sizeForItemAtIndexPath correspond to the three cells to be (re)displayed in step 4. As you can see, the app calls and returns from insetForSectionAtIndex and then crashes on a mysterious call to [NSPlaceholderDictionary initWithCapacity].

Here's my cellForItemAtIndexPath: method:

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView
                 cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    NSLog(@">>> Entering %s >>>", __PRETTY_FUNCTION__);

    TPXFilePlayerCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"filePlayerCell" forIndexPath:indexPath];
    cell.backgroundColor = [UIColor clearColor];

    [cell setTag:[indexPath item]];

    [[cell slider]setTag:[indexPath item]];

    NSNumber *newGain = 0;

    if ([[self openSketchbook]mixerGainSettings]) {
        if ([self.openSketchbook.mixerGainSettings count] >= [indexPath item]+1) {
            newGain = self.openSketchbook.mixerGainSettings[[indexPath item]];
            [[cell slider]setValue:[newGain floatValue]];
        }
    }
    NSLog(@"<<< Leaving %s <<<", __PRETTY_FUNCTION__);

    return cell;
}

What could be causing this or how might I troubleshoot this?