Valid question. The result in this case was getting a patch that was already committed into the development branch, just not yet released.

I actually did debug it (i.e. I found the cause of the bug, just didn't know whether fixing it in the most obvious place wouldn't break anything elsewhere - it occurs it might) but my fix would probably be suboptimal and I'd probably waste the developers' time with a superfluous bug report (and maybe the suboptimal patch too).