This bug also occurred in Odessa at the CIS-2013 tournament, and in several games at once. Apparently, nothing has changed in the game engine over the year. :(
If we are going to call it a bug, then it's a bug in the HD mod. Without it, this bug doesn't exist. In reality, it's more of an incompatibility issue between the game engine version and the HD mod.
What specific conditions lead to this bug? Does it only occur in battles in the Dungeon, or in any battle, on any type of terrain, or a specific one?