unblank screen during call?

Hi,

I dont know if my phone (Iphone 4, 4.01) has always done this or not, just that in the last few weeks it's really started to annoy me.

When in a call, when the phone is near your face the proximity sensor kicks in and the screen turns off....great...except it doesn't come back on again when I take the phone away from my face. this means that I have to turn the phone on, and if I do that it takes me to the home screen and I have to press the tiny little strip at the top of the screen so that I can get the phone call screen back again if I want to put the call on hold, mute, end the call etc etc.

is that how it is supposed to work or isn't it supposed to turn the screen back on again if there is nothing near the proximity sensor?

is this a recognised issue?