Could be some faulty switches, but you can also adjust the debounce on the keys. somewhere on the F layer (I think F10 and F11) there should be symbols on the front of the keys, they adjust the debounce up or down. That should do a software fix for your problem... mind you probably not the best solution, but its possible until you can/are willing to solve it further =p
Do note however, too much debounce might reduce the speed at which you can type at if its set way too high.