It just so happened that it was 1) crashing and 2) apparently scanning outside of the directories I told it to scan in.
I started a thread on the Firefly forums.
Taking down every issue one step at a time, it proved that I was in err and that mt-daapd was actually working OK.
What happened was that in one of the directories it was scanning into I had an old backup of root's home directory that I've forgotten about. And there, in '/foo/backup/root/.wine', there was a naughty symbolic link pointing to '/'.
lrwxrwxrwx 1 root root 1 2007-11-11 11:45 /media/sda9/backup/b4gg/root/.wine/dosdevices/z: -> /
So, kids, my advice is that the next time you feel like starting swearing a software for "not doing what it's supposed to do", you double- and triple-check your setup first; there's a big chance that you were the one doing something stupid in the first place. :P
So far, after discovering this... user fault, mt-daapd seems to be working nicely for me. I use the svn-1696 release.