Yea I've had that happen to me as well. I will unlock my N6, tap my email icon (it kinda gets highlighted), and then tap it again to open. Doesn't do this every time, but most of the time.
a month later and still the issue with no solution. anybody else with this issue? this is very annoying when im in a rush. also sometimes when i unlock and hit the phone button and its non responsive..i will hit it again. and then it will dial the contact box i clicked on.