The one other possible glitch in this mix is that I have a spamcatcher called Email Protect. I'm sorry, I don't know enough about this stuff to know if it could be a problem, but I thought I should mention it.
Lucy, I don’t know that program, but i sure can imagine it is the problem?
Thunderbird has it’s own Junk mail feature that works well.
Try disabling it from running and Thunderbird should have no reference to it in account settings I think.