Possible bug with mouse buttons 8 and 9 (part2)

[info at datakoti.com]

Regarding my previous email, I am willing to do some debugging (I have
some experience with ddd) of the source if this indeed turns out to be a
bug. If for nothing else, then out of spite towards FSF, which in my
opinion has totally lost any grip on reality.

Of course I need some hint on where to look at.