The icons on the bottom bar have disappeared in both Exchange and gmail on my iphone 5.
The icons allow me to reply, forward or delete and email.
Icons used to be there, but now the bar is blank.
This doesn't seem to be a setting.
All you'll lose is about 3 minutes of your time. Just hold the power button down until prompted to slide to turn off. Slide. Wait for the circle to go away, and once it's off, hold the power button again to turn on.