ToME: the Tales of Maj'Eyal

My archmage has a level 4 (effective 5.2) teleport spell. While using it in a dungeon to escape a mob, it fizzled and teleported me straight into the boss room. It was close, but I managed to escape. Now I'm paranoid about using teleport if it's unreliable. What could cause it to fail?

I've checked my gear, no arcane disrupting items are equipped. I've tried testing teleport in town. I haven't been able to fail or succeed consistently.

Which dungeon?

Tempest peak, though it has happened in other dungeons I've tested it in, such as the maze.