Stopped and started the program. It took a while, but it started to work again. That doesn't always work, though. (The previous time I ran into this, even restarting the entire computer didn't fix it.)

It seems that clicking on one of the entries in the list to open the filtered e-mail may very well also "unlock" the bug. I noticed that the disabled buttons 're-enabled' immediately after opening one of these messages.

Any idea when that 2.0 version is coming out? I would be interested in evaluating it....