There is a world of difference between what the processor can see in a
scanned keyboard, and the classic demonstration of this using the switch to
clock a digital counter that can do 10-100 MHz counting.

Other factors come into play like pullup resistors on the rubber keys, since
they are variable resistors. If the pullup is too hard then you'll get
symptoms like that, or if the rubber is wearing out, or damaged in some way.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist