I'm recently finding it happen quite often (once/twice every day).
The clock just disappears from home screen! If I click on the place of clock, it does open the clock app but the digital time is not shown on screen!
It also bring another problem. When I press white menu key, the menu did not appear! Only way to make menu appear is via long press on white key and select menu from running task bar.
The phone works ok upon restart.
What went wrong? My FW is v21 (later versions not avilable for my phone code).