Mozilla Thunderbird Hotkeys unconfigured

I own a Samsung N120 and my Thunderbird was working fine under Ubuntu 9.04

When I changed to Ubuntu Remix and I open a message on a new window and I try to use the hotkeys like B (back) F (next message) or oven the arrows keys to scroll down the message, it gives the order to move the message to the trash folder, it only happens when the window is maximized in a separate window, when I am reading the message without opening in another window the hotkeys work fine.

I tried several times doing the install, and also go back to Ubuntu 9.04 and then the problem was there, so I believe the problem is in some configuration file but I don't know where to fixed.