Probably a glitch; I say enjoy the free money!
I've got to admit that one of the things I've found I enjoy most about playing Daggerfall is finding all these weird glitches and exploits that Bethesda didn't fix. It's actually pretty interesting to me.
And the best part is, Beth is still the king of bugs! After spending 5 minutes withdrawing my 200k from the bank so that I could summon Hircine because it would glitch out if I took over 5k out at a time, I decided to switch over to Skyrim and collect a few dragon souls...only to find that the dragon didn't give me a soul after dying and seemed to be possessed by a spirit as it twitched around after it died. That's how I knew they were by the same company!