Had not been to Markarth until tonight. Entered the city, killed the Forsworn hitman, talked to a few people, and tried to enter A&S's. Door is locked. Door is locked all day and all night. Tried leaving city for a couple of days and coming back. Still locked 24/7.

Tried disabling any and all mods that might be sources of issue including but not limited to Unofficial Patch. Still not open.

Created mod that unlocks door. Intro scene plays, but then both players will threaten to call guards immediately after.

Since this happens with mods enabled and disabled, it sure seems as though this is a new feature of 1.6