I've noticed this quite a bit when I'm playing.
I think it's caused by lag, but sometimes after a while of playing my "/" key turns into a lower case Greek letter "Theta" and it changes some of my other keys too like my "?" turns into an uppercase E with an accent aigu (French).
It gets quite annoying over time as I have to reach over to my numberpad and hit the "/" there where it still works. Then when I have to airstrike or check my ratio it's a pain in the ass.
Anyone else have this problem?