On Windows, bind.test still passes 100 %:

Total	523	Passed	520	Skipped	3	Failed	0

About the change in the return value of Tk_CreateBinding I'm very slightly uncomfortable because this function is part of the public interface of Tk. Even if binary compatible this change should be clearly mentioned in the TIP I think. Given that "Mask" is typedef'ed in I believe it will be fine.