I am able to reproduce this bug with Gwibber 3.2.1 in Ubuntu 11.10, and the noted method to get scrolling working works as well. This occurs for me 100% of the time.
I've just recently moved from Maverick, where this bug does not exist, and GNOME2 with Gwibber 2.32.2. I am currently trying to use Unity. PC is 64bit. Happens on my wife's computer as well, with Ubuntu 11.10, where she is using Cinnamon 1.3, also 64bit.