The .66 BBM has this glitch and even if you use app world and dl the old .57 version it is still present. Here is a workaround that works. In BBM Chat group hit the BB button and hit New Chat, then hit cancel and your keyboard stays up. You do have to do this every time but it does allow you to still chat in groups.
FYI- There is a new BBM that is in beta right now that does fix this glitch. So it is coming soon.
Other than that I really like this OS.