Read the man of usermod, the -G flag is used to SET (not append) all additional groups for a user. So as you didn't specify wheel in the -G flag wheel was removed even though you were originally a member of wheel.
> I did an `su` and logged in as root, emerged some stuff, and did a > `usermod -G games joeljkp` to add myself to the 'games' group. I then -- [EMAIL PROTECTED] mailing list
