I don't know if this is a bug, but when I logged on I lost my "Temple key"

It's not a bug, I don't think. It's a quest item.. and just like the rest of the quest items, it disappears with a reset!

HB is right, i asked DM about this after i lost my Temple key

You should be getting a message when you lose the key, that it's being cleaned up by the quest system.

This is not a bug.

IC'ly, the lock is regularly changed by industrious *spoilers*