
My workaround is to turn the manual camera and smooth movement in combat off -- I haven't seen it happen since I toggled these off, so the bug seems related to camera movement in the way I described above. (Side bug: smooth movement with manual camera off leads to very odd behavior (creatures all over the map, attacking in borders, etc.).
TLDR: To avoid the bug, set UseCombatSmoothMovement to false, set useManualCombatCam to false.
Edit: But with these settings, the combat map is locked to the 0, 0 left corner, which can make fighting and visibility difficult because a portion of the map is always under the combat log...