bug#36779: 25.1; mouse click not recognized for frames with large left position

[Eijiro Sumii]

My point was that we should try explaining the reasons and the fix
both concisely and completely, such that there would be no reason to
read about the details, none at all.  IOW, PROBLEMS should be
self-contained.

I'm afraid that is just not possible, at least in this case.