I had that issue with key presses with both firmwares. I'm using lbook now and I went and removed some files, redid my library and it's gone away. I notice it the other day it's seemed faster and no key misses.
I don't know why though. I removed all MOBI/PRC files from my card, EPUB only now. I removed the subfolder I had in my fonts folder and a few fonts but other then that I didn't change much other then adding a dictionary. The reader seems really fast now. The pages change so quickly too in Cool Reader.
I have no clue what I did to fix it!