typing up a bug report, now. I can duplicate the period key ceasing to function, and the fix.
Under X, I go to System Tools, then Input Setup. Change Right Mouse Button to R Shift, then select Okay and exit. Restart X.
But then you decide you want to use R Shift to type Caps, like I did, because it is awkward to use L Shift all the time. Well, you go back, you change it to the Fn it was defaulted at. Exit X and save. Oh noes! The period key doesn't work anymore!
To fix it, I started X again, opened kernel.map in SciTE, changed the last line to read keycode 112=Shift, saved it, exited X, and reboot. Then the period works again
Crap, I forgot to add to the report that I use the SL-C3100 It is Bug Report #357