I try to enter Deadmines with my alliance alt lvl 18, but I can’t find DM in the list, kind of odd when I got the quest The Forman and it show as yellow.
Had to log into my horde character lvl 15 to see what level DM is this days in Classic Cataclysm, it show Deadmines 17-21, Ragefire Chasm 15-20.
So my guess it’s a glich or bug, just annoying when you try to do all quest in an area incl. Deadmines.
The dungeon finder is a bit bugged, there is a number of dungeons just straight up missing, or disappearing at way too low levels, and it’s not just low level dungeons either, as soon as you hit max level, most normal mode dungeons just disappear from the dungeon finder, including max level ones.