Weird recursion in setting the default file manager in antix/icewm

I've installed antiX Linux 19.3, and I want to change the file manager - for the first user and by default - to something other than the annoying rox (sorry, I just don't like it). So, I've installed pcmanfm, went to the Control Center pressed "Preferred application" and got a dialog with paths of .desktop file. Ok, so far so good. The file manager one is: deskto-p-defaults-follow-fm.desktop, suggesting the setting is actually taken from elsewhere. Now, that .desktop file runs:

desktop-defaults-run -fm --follow

there's a matching desktop-defaults-set, but - if I run that one, I get the dialog I saw before. So it's as though there's a recursion without anybody choosing a file manager. I then looked into desktop-defaults-run, and it seems to be looking for a file-manager-related .desktop file, which itself runs desktop-defaults-run -fm --follow. Unless I've mis-parsed the script (which I may have - it sources some more scripts when it starts). What's going on?