If it was blindness by the actual blindness/deafness spell with the little icon in the corner, that'll be a beamdog issue to fix unfortunately. They will want screenshots and probably a copy of an area / module and logs, or some other means of reproducing it easily.
There are some similar situations that can cause invisible enemies to attack and be unrevealable - certain tilesets such as the temple of Harvest if the mummies get into the centre corridor and Malthor with whatever he does, if your game has begun to crash out and enemies / doors / transitions start failing to render, the darkness / ultravision bug when either spell is cast on you while affected by the other and ultravision fades.
Since the enemies fail to render at all as entities, its similar to when someone has a door override that removes the models - if its not there it doesn't exist, and can be walked through.
Usually if its stealthed creatures and regular blindness/deafness, creatures are still treated appropriately and have their collision models, so I have to admit it is rather peculiar, but not entirely impossible, and in any situation that invisible enemies may occur, is unfortunately mostly outside of dev ability to fix since they're limitations&bugs of the game engine NWN uses.