The "Spawning in Level 100 of different Dungeon" is a new bug to be honest. Before, when you saved in a dungeon and loaded your save afterwards, you spawned in the Sewer Dungeon's 1rst Floor, if I remember correctly. Sometimes you could even get stuck in the ground and unable to move from that spot. That said, even with that bug you still had the possibility to leave the dungeon just by using the entrance, with the, I suppose, Castle Ruins Dungeon you need to use the ladders... Or I missed the "press E in front of the door to interact" option...