Hello,
Since I just advocated using nnvirtual, I thought I'd give it a go.  I
created a new virtual group (G V) and then customized its select
method to be (nnvirtual "^nnfolder"), which I though would be quite
fun as it would then *all* my mail.

It looked like everything was working nicely.  It took about 20
seconds to open the group with about 10MB in c.1000 messages and I
played around to see what I could do.  I tried to see if I could use
it as a poor-man's search engine, and I could, with M-s, then I tried
to leave the group (by pressing 'q') and it started trying to expire
various articles, and I got;
(wrong-type-argument listp 240)

Here's the backtrace: