Looks like we had a bug sneak in when I added my Objective-C categories to support the iPhone project. I was aware of the linking problem with static libraries and categories, and the -ObjC linker flag appeared to fix the problem, at least in the environment I tested it in. Unfortunately, I've received bug reports from users and after testing it under Xcode 3 found the same - unrecognized selector in spite of the -ObjC linker flag.

Turns out there is a known linker bug with -ObjC. (I suspect this has been fixed in Xcode 4.) I didn't want to use -all_load or -force_load if I could help it, so I took another approach: I declared a dummy C function in the source of each of the categories and call it from the library's initialization thereby forcing the symbols to load. This works with both versions of Xcode we are using here. If you're building for iPhone, please grab the new source and let me know if you run into trouble. There are a few more fixes and updates as well as the first pass on the particle system rewrite. I'll be doing a blog post about particles Soon™.