You might have some "sticky" keys. Have a look very closely around those keys and make sure something small hasn't fallen between the keys preventing them from operating correctly.
You may have also had some liquid spilt on that section (not by you) and you didn't realise.
Unplug the keyboard, turn it over in the air and give it a good shaking (don't beat it or hit it) just shake it and see if you can hear anything possibly lodged in there...maybe a midnight snack