Steps to recreate the defect.
1. Lock the phone.
2. Send a text message to your number (Nokia N8).
3. When the text message is recieved the screen of the N8 displays the work "popUpClock" in the top left corner and the "time, Battery, and signal" icons on the right top corner.
4. The above message disappears in a split second and the screen remains blank for almost 2-3 mins before shutting off again.
The best way to check the duration of the blank screen displayed is to keep the phone in dark.
This bug could be one of the reasons for the battery draining for some users who recieve loads of text messages in a day.