I have the same issue with Monospace Regular 9.0 on Ubuntu 12.04.
When I choose 10.0 as font size as workaround, the setting is only effective until I exit KDiff3, then KDiff3 forgets the font setting because of bug 1074468.
This is quite annoying when launching KDiff3 for editing multiple files from a script.
Thus I have to choose the font for each of the >100 files to diff. :-(
I have the same issue with Monospace Regular 9.0 on Ubuntu 12.04.
When I choose 10.0 as font size as workaround, the setting is only effective until I exit KDiff3, then KDiff3 forgets the font setting because of bug 1074468.
This is quite annoying when launching KDiff3 for editing multiple files from a script.
Thus I have to choose the font for each of the >100 files to diff. :-(