Gnome 3 keyboard lock up?

Usually when I'm on GIMP trying to edit some graphics or anything, I sometimes hold down the shift key and when I go to undo something using ctrl + z, my keyboard instantly starts to lock up and makes the error beep and the screen flashes (cause I have visual alerts on). And when this happens nothing on the keyboard happens to work, not even the caps lock keys or delete or esc. When this does happen, I can hold down a character key (A or B) and I do get a string of characters but thats not very useful. A reboot of the system and the keyboard works fine again but I want to know why this usually happens and how I can fix it so I can get on with my graphic design work. Can anyone help?