You can't unequip unless you have other equipment already in the station.

hmmm, this is new. I unequipped a ship last night with no other equipment in-station...not even a different ship to put the equipment into.

unequip all works, just not the normal unequip (atleast for me).

What sector were you in? I'll need to check the logs for that sector. Also, what time? so i can narrow down the search.

I didn't know what sector I did it in or when, so I just did it at 6:11:50 EST. In the Ukari Command (L14) station (repeated it 10 times or so, so it should be easy to spot in the logs).
It gives me an error of "Station transaction error: Only cargo can go into cargo slots." and it appears to be infinitely reproducible in any sector/system/station.