HTC Desire :: Message Sometimes Received Without All Notifications

Had a Desire from Orange for a couple of months, one of the most annoying issues is that sometimes when I get a text, it doesn't register all the notifications when the phone is idle: I always get the notification sound / vibrate. Sometimes I don't get the flashing green led. Sometimes I don't get the message summary on the lock screen. So if I don't hear the message come in I often miss it. I'm constantly having to wake up/unlock the phone just to check the actual message app whic is a) really tedious and b) probably not doing much for battery life. When I say sometimes, it's probably about 10% of the time, and one or other or both problems can occurr. I can't find any correlation other than having the messages app active when the phone sleeps *may* exacerbate it, but I'm not totally sure and it definitely does happen when the app is not running too.