Version: 2.0.5 (using KDE 3.5.5, Debian Package 4:3.5.5a.dfsg.1-1 (testing/unstable))
Compiler: Target: i486-linux-gnu
OS: Linux (i686) release 2.6.17-1-686
Copy the 10 in this sentence and paste it into kcalc. Hit "Mod" and "3", then "=". It will display 0, though 10 mod 3 is obviously 1. kcalc reports 0 for any mod operation where the first number is pasted.
Confirmed on r582183 (hrm, that's a bit old now)
Just fixed this in the sourcecode for KDE-3.5.6. Thanks a lot for reporting it!!