After the reinstall, my Logitech Marble Mouse (which is a trackball), has gotten new keymappings.

Using xev, I get the following default mappings (btw. it has "only" nine buttons, as opposed to 11 at work).
1 - Left Big (LB)
2 - Left Big + Right Big (M) at the same time
3- Right Big (RB)
4 - Not used
5 - Not used
6 - Not used
7 - Not used
8 - Left Small (LS)
9 - Right Small (RS)

Now, what I want, is to have paste on LS, so I do:
xmodmap -e "pointer = 1 8 3 4 5 6 7 2 9"

Again, the mapping can be seen with xmodmap -pp