HTC One S :: Doesn't Wake Up After Losing Signal?

if this is a 'feature' or a fault. I find that if my phone loses signal (i.e. going through a train tunnel) then it does not automatically reconnect once back out in the open air. I didn't realise this and wondered why I was not getting email feed on my phone. I pressed the top button to activate the screen and it briefly showed no signal before quickly registering full signal and then downloading about 15 emails. It seems that I have to wake the phone up after signal loss or else it will just sit there doing nothing. With the best will in the world this is going to be difficult - it is possible to lose signal fairly briefly and not even realise in which case the phone could sit unconnected for hours before I noticed all was not as it should be. Does anyone else experience this? I have had HTC phones in the past (a Desire HD just prior to this One S) and have never come across the issue before - my phones have always instantly reconnected as soon as a signal becomes available