I had this in r64.

This is a classic in the banshee room. Guess the code for that area specifically is somehow faulty.
Also, I seem to encounter the lower horizontal rows as well, more often than any other.

Well, corridors can happen only at certain rows... Some specials areas which I presume are not created by map part of the code (like vaults, shops, banshee room) sometimes com in conflict with this. Vaults sometimes have two square wide corridors leading to them and... banshee room sometimes end with a corridor just below (or above or west/east) the room.
Problem with banshee is aggravated by the fact that typically there is like 4 corridors leading to that room.

Anyone still having this in R65+ ? The code now looks very safe :-)

I have had secret doors in the corners of the room in R65, but not sure if there was an entire row.