I ran into this problem multiple times a few weeks ago when I tried to play. Fired up another Drang campaign and it happened again. I actually saved it this time. This is a new install with 1.06a and QF1. The first time was on a different install with just 1.06a.
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[ATTACH]21107[/ATTACH]
Essentially, there is some kind of overflow bug during battle resolution that prevents proper capture of regions or destruction of units. This always happens when assaulting enemy structures under siege. 1 enemy unit overflows or something, and the attackers continuously assault these ghosts multiple times until the turn ends. In the turn above, I assault the "ghost" horse artillery 6 times, inflicting hundreds upon hundreds of hits, but suffering a handful in return. Of course, this also results in most of my generals dieing due to the problem with generals dieing in low intensity battles. It also sent turn resolution from under 3 minutes to 10+ minutes. Each one of these battles takes over 1 minute to resolve. In all of the instances I've seen this bug, it is just one enemy element taking hundreds of hits per battle and not being removed. Hopefully it's repeatable, I included the turn it happened and the backup turn in the .rar above.