well, if GetOpenClipboardWindow() returned anything != 0, the tooltip will be shown 100%, it can't be any rarely
It works rarely for me, that's all I can say. Would it perform more predictably if it were to call OpenClipboard() before GetOpenClipboardWindow() (and of course CloseClipboard() later)?
it would be nice if you can describe any way to reproduce your problem on practice with code example
I'm working on getting a reproducible example but the problem is too intermittent. That AHK tends to need kludging with Sleep, which optimal duration varies widely, is a fundamental issue or limitation.