Every time I log in the Dalaran Hearthstone keeps being created and placed in my backpack. I have to keep on delete from my backpack. This happens on all my characters.
There is a new quest that just came out that tells you to go to Dalaran to continue it. Therefore you are given a one time use hearthstone to make it easier to get to Dalaran. This is intended.
And it’s going to keep happening until you do at least the first quest step. (Hearth to Dalaran.)