Hello everyone.
This is my first post on this community...and I hope someone will find it helpful.
I don't know where the bug has found its origins...but for my iphone 4s and another iphone 4 both with ios 5.0.1 i found a solution.
Instructions follow:
-Go to settings-->notifications
-Disable notifications in lock screen for: email, Messages, viber and whatsapp.
-Reboot your phone (Turn off and turn on)
-Enable your notifications back as you prefer...
-that's it.
It worked fine for me and a friend of mine...please feed back if it works for you too.
I apologize for my english.
Giordano.