To & Subject fields disabled in compose window

[John Smith]

The first time a compose window is opened after starting Thunderbird, everything goes fine. But if I try to write a new message, the new compose window which shows up has its To & Subject fields disabled, I can only write the body. This occurs regardless of the fact that I actually send the first message or simply close the window. The only way to send a new message is to restart Thunderbird.

System is Xubuntu Lucid 10.04 with Thunderbird 10.0.2. I've recently installed this ppa and upgraded from stock Lucid version, the problem is present since then.

Thanks!

[John Smith (johnsmith-launchpad)]

Sorry, I should have checked first: the problem was caused by an add-on. The problem disappeared when I removed it.