I had a positive gold amount, then got hit with Plague, and chose the 'spend gold to cure without losing pop' option, ending up with -67 gold. I then sold a few items, ~60 gold worth, then saw my debt was now -127 gold. Apparently the profit from selling was added to debt instead of subtracted. It was handled as if I had a positive gold amount and the sale profit added to it.
I reloaded but the plague event didn't recur, so no screenshots or replication of this. Will add to this if it does/doesn't recur should I go negative gold again.
