This is most likely a problem with the debug information rather than with the generated code, which is why your app runs correctly but the expression evaluator in the debugger fails.

The debugger always tries to read the least amount of debug information it needs to in order to do whatever you ask it to. So until you do something that causes us to read in the two modules that have disagreeing debug information, you won't see this problem. That's why it sometimes happens and sometimes doesn't.

Anyway, please file a bug about this with bugreporter.apple.com.