This happens to me at random throughout the game; most noticeably during the Doc Roberts quest as well. Double-tapping the space bar (to exit and quickly re-enter turn-based mode) is the only fix I've ever found, at the expense of giving the bad guys a free turn.

I don't know what causes the glitch either; my guess is that one of the attackers or NPCs has enough movement points left for the AI to initiate a particular action (such as casting a spell or running toward your PC) but not enough to finish it and let you have your turn. It seems to happen most often when there are four or more NPCs/attackers for the AI to handle. Processor speed doesn't seem to make any difference, so it's probably an issue with one of the in-game algorithms.

much obliged for the response. guess i'll (we) will just have to continue the space bar fix

Retoggle turn based combat is the only way to get through it.

Someone on terra-arcanum I think said it has something to do with an out of area creature trying to take a turn or a creature that died trying to take a turn. Because this is Arcanum, no one really knows what causes it for sure.

This makes sense.