The default Xmodmap should not contain a workaround for XFree86 backspace bug. The bug should be fixed in the X server (it's a one line fix). Messing with backspace causes keyboard to misbehave when vnc is used due to differring keycodes (character '5' doesn't work).
what is your proposed fix? Without this Xmodmap, and if you aren't using xkb extensions, motif apps have backspace problems.
*** This bug has been marked as a duplicate of 7841 ***
The proposed fix is in the bug#7841 as you have noticed.