You may remember that CEP 2.3 included the fixes to the Dwarven Hall tileset from Project Q, which corrected numerous visibility issues.
The problem seemed to be fixed in both 1.69 and EE at the time.
However, there appears to be a new problem in EE now (in .13 and .14, at least).
I made a demo module.
If you run it in 1.69, the PC can hang around in the corridor all day, but nothing happens.
In EE, the hostile creature in the next room opens the door and attacks.
On both platforms, the PC can see into the room before the door opens. This is strange, because in the full module in which I first discovered this, the room is invisible, even though the tiles are identical (apart from the southern end of the corridor, which opens into a larger areas). Another clue that something is horribly wrong!
I have reported this to Beamdog, but I’d welcome any insights from this forum, as I’m not sure that Beamdog will see this as a backward compatibility issue.