iPad Keyboard Rendering - Missing Letters / Keys
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I have been working on an app for a number of months now and a strange bug has appeared in the last week or two. After extended use of the application (20-30 minutes), many of our custom labels (based on UILabel) cease to render correctly (some will just appear blank). Interestingly, bringing up the keyboard in this situation shows the following:

![enter image description here][1]

I've tried a number of tweaks over the last couple of weeks to various parts of the codebase with no avail and I was hoping that someone here might have stumbled across a similar problem before and/or might have some ideas of where to look for a solution.

We are using lots of CoreGraphics calls within our custom labels to render some pretty complicated annotated strings and have a fair amount of traffic going back and forth to a server in the background on another thread. With regards to memory, we are using ARC and while we're keeping about 5-10Mb of raw data in memory at any one time - I can't imagine that anything else is chewing up loads of memory.

Any advice on where to look would be greatly appreciated.

  [1]: http://i.stack.imgur.com/AuLgX.jpg