i see that you have no solution for days so, although i'm "the last person in position to offer help" (very new to sabayon myself) thought to, point to the direction, if not able to (and it is virtually impossible i think, for anyone, with the information provided) give a readymade solution as such..
the mouse is, afaik handled by x.org mostly (very scientifically said, isn't it??
) and the problem that you are experiencing is most probably rooted there..
if i understand correctly, you are having this issue in a live kde session..
what i would do is, test another flavor live (xfce for example) and see if it is a kde specific or a lower level problem.. btw.. as trivial as it may seem, doing a checksum on the iso that you're booting wouldn't hurt..
as you most probably know, sabayon is based on gentoo (or more precisely, it is gentoo testing with sabayon overlay and the entropy package manager) so, searching for solutions to problems extends to the wider gentoo universe.. example: https://forums.gentoo.org/viewtopic-t-9 ... d05dd6256c
if the problem persists in the live session(s), i see a high probability that it would be gone "by itself" after an install on metal and an update..
best of luck to you, with pointing devices, and everything else.. hope that this doesn't discourage you from using this fascinating distribution..