Version 1.00 - this seems to be a new bug, version 0.99 does not seem to be affected.
Upon entering the fortress basement from the sewer for the first time on this version, the bats get stuck. They attack once - and then after this attack, they then rise up to the ceiling and stay there, and don't attack again. All red bats behave in this way. If Edgar is able to reach them (for example, by jumping) then they can still be defeated as normal.