EXC_BAD_ACCESS when object released mid-function - ios

Question

I have a class with a property
#property (nonatomic, copy) MyObject *currentObject;
and a function that looks like this:
- (void)handleExternalChange {
#synchronized (self) {
MyObject *newObject = [self.externalStore getObject];
//Business logic...
self.currentObject = newObject;
}
}
I am seeing a crash objc_msgSend() selector name: copyWithZone: occasionally when i hit the self.currentObject = newObject line.
I presume this is because the externalStore released the object returned by getObject on another thread and by the time it got down to the setter it was gone.
Does this conclusion seem right? If so is there a recommended way to fix this?
UPDATE:
Here's some of the stack trace
Application Specific Information:
objc_msgSend() selector name: copyWithZone:
0 libobjc.A.dylib 0x000000018149ef30 objc_msgSend + 16
1 libobjc.A.dylib 0x000000018149c2d4 objc_setProperty_nonatomic_copy + 44
2 MyApp 0x0000000100115cb4 -[MyClass handleExternalChange] (MyClass.m:117)
3 CoreFoundation 0x00000001829ee22c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 16
4 CoreFoundation 0x00000001829ed930 _CFXRegistrationPost + 396
5 CoreFoundation 0x00000001829ed6ac ___CFXNotificationPost_block_invoke + 56
6 CoreFoundation 0x0000000182a5cb9c -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1500
7 CoreFoundation 0x000000018292fbf4 _CFXNotificationPost + 372
8 Foundation 0x00000001834366bc -[NSNotificationCenter postNotificationName:object:userInfo:] + 64

Answer 1

MyObject *newObject = [self.externalStore getObject];
That method shouldn't be named get* anything, but that isn't likely to be the cause of the issue. Nor is it likely to be a threading issue (at least not directly).
This sounds more like there is some state related to the copyWithZone: that isn't handled correctly. How is the copy method implemented? Specifically, is it correctly copying all state and bumping reference counts or does it try to cheat by doing some kind of a byte copy?