I have an app that appears to run without problems in normal use. The Clang Static Analyzer reports no problems either. When I try to run it in Instruments, it fails with an unrecognized selector exception.

The offending line is a simple property setter of the form:

self.bar = baz;

To figure out what's going on, I added an NSLog() call immediately above it:

NSLog(@"class = %@ responds = %d", [self class], [self respondsToSelector:@selector(setBar:)]);
self.bar = baz;

On the emulator (without Instruments) and on a device, this shows exactly what I'd expect:

class = Foo responds = 1

When running under Instruments, I get:

class = Foo responds = 0

I'm stumped as to what could cause this. Perhaps a different memory location is getting tromped on when it's in the Instruments environment? Can anyone suggest how I might debug this?