Dead buttons after ios 7.1 upgrade

Hi all, got a strange one. Immediately following the update to 7.1, you can touch a key for 10 seconds before it becomes active. Filling in a password is the same way, can't type for about 10 seconds. while making a call, you cannot open the speaker phone for the same 10 seconds, keys are inactive.

The iphone 5 is over a year old, I saved everything to icloud and restored the phone. Same problem during the new boot up following the restore. Apple store has no clue, anyone here have an idea?

Thanks in advance! Mark