Leaked NSString from class_getInstanceMethod

When I use the function class_getInstanceMethod() in +load in a =
PDFDocument category, I get the following message in the console log:

*** __NSAutoreleaseNoPool(): Object 0x100404b30 of class NSCFString =
autoreleased with no pool in place - just leaking

I really don't do anything else than what I said (at least in a test, =
the actual code I would like to have of course does a bit more, but =
that's not relevant).

this makes absolutely no sense to me. The function is a runtime method, =
so it should never even use any Cocoa itself. So what NSCFString could =
this actually be? It also does not happen when I do the same in =
categories on other classes, including PDFKit classes. Anyone has an =
idea?

thanks,
Christiaan