When using dungeon finder to level up, players who pick the healer specialization and meanwhile roam in the open world in their DPS specialization will have said specialization be changed to Healer automatically by the system. This sets their mana to 0% as they spawn inside the dungeon.
I will have to agree with that. I don’t find any other explanation why a healer should be forced to start a random dungeon group with 0% mana if they choose to use their DPS spec before entering the dungeon. It’s literally only for normal and heroic dungeons people use while leveling.
Changing specs anywhere will do the same. I don’t know why but it is annoying, my guess would be something to do with the way the stats work, it’s like when your pet gains a level it’s health is dropped to 25%.