Xperia Z - Airdoird "stops" if Display turns off

Last Friday i got my new Xperia Z from SonyToday I installed Airdroid and found a bug.

If I turn off the display (or display times out) Airdroid stops and I can do nothing via my browser.
If I reactivate the display it works until it turns off again.

Please have a look

never mind


I forgot that Stamina Mode

what is "stamina" mode? I have same concern.