Mail behaves very very strangely...

I've just set up Mail and in the beginning both my account and my wife's account were fine. Everything worked perfectly, junk mail was colored very precisely..etc.
I also changed the size of the font, changed the junk filtering to go straight into the Junk box..
After maybe half an hour i opened Mail, and when clicked on my wife's account, my account also got highlighted and both accounts have opened at the same time. I kept clicking trying to open only one of the accounts, but most of the time both accounts highlighted and even the "inbox" and ".mac" trial account(which i should delete anyway)..all are getting highlighted.

Also the left pane is for some reason in light grey. I don't remember if it's normal.
What's wrong here ?

Thanks!

a little correction, sort of...
After I posted this problem, I went back to Mail to check. Now it was normal, everything was fine. Still, I'm curious what could have been a problem ?
In any case, I removed my .Mac trial account there.
Anybody encountered this type of problem ?

Had you rebooted between your visits to Mail? If not would try booting from install DVD and going to Disk Utility and running Repair Permissions from there.

I didn't know it was on DVD, downloaded from Apple.
It looks ok now, though.
Should I reinstall it from DVD ?

I have another little problem with Thunderbird, which I want to trash.
I use AppDelete but every time I drag anything with the name "Thunderbird", it rejects. I tried to drag there the .dmg file, the disk on the desktop.., all rejected.
I would use TB own uninstall, but don't know where it is located.