Definately an exploit. However, I would also like to know the intent behind the second duchy flip. Perhaps the character was trying to cash his chips and keep whatever titles and lands he had left. Doesn't take away from the fact that he exploited a bug however.
The realm of Solaria had no money left, no chance of surviving. Sevastian wasn't trying to salvage anything but allowing the remaining members of Solaria a chance to keep living and fighting.
If its a bug exploit, I'm fully prepared for whatever repercussions come of it. I would like to know how the duchy that held the capital was able to switch in the first place though.
