I haven't yet been able to get a good report from drWatson, sorry. But I have some interesting observations to share:
First, I don't think that it's of any use to anybody, but the error comes from address 0x00481f93 in the program, :0xc0000005. Access violation reading 0x010b0108
The same thing happens no matter what the s key is bound to. And it seems to only be the s key.
The winquake version didn't crash instantly, I think. Instead it printed garbage (SSSbbbcehlnnnooonnmlonllmnno) AND listed a few demos that lie in a directory I wasn't browsing at the time.
At that time I checked my disk, but it turned out to be fine.
And here's another observation, perhaps the most interesting one. The crash only occurs if I type s when I have browsed to the quake root, and if there are 12 or more subdirectories in it. I removed some directories, pressed s, and it didn't crash. I created a 12th directory, pressed s, and it did crash.
I'm perfectly willing to accept that the problem is something on my end. Looking forward to the next version of JoeQuake to see if it behaves in the same way!