Double letters while searching on launchpad anyone?

This could be a known problem (more). Workaround (fix?) for that is the killall Dock command entered at the command line in Terminal.app; restarting the Dock. Some other things to try, if not: see if this happens when booted in Safe Mode to try to eliminate add-on software, then try setting the keyboard repeat to slower and see if that reduces or avoids the problem, and try a different keyboard — preferably wired and not Bluetooth — and see if that reacts similarly.