The usual apologies if I missed this when searching the forum prior to posting. Last 2 turns the men disabled has gone into negative numbers. Last turn Soviet, this turn both sides.
Game is 1.09 (started in earlier version)
about turn 120 (Oct '43)
Unfortunately the number of disabled men fluctuates, because that's a pool, not a statistics. Some disabled men each turn are returned as healthy and some are removed as killed.
In your case more men were removed from disabled pool than added to it. Happens when there is little combat and the pools are large.