I had the following endeavors:
Universal: Nimbus Dance Competition 0/1
Easy: Defeat Vaadwaur (Ground)
Medium: Defeat Captains (Ground) 0/2
Hard: Destroy Tzenkethi Ships (Battlezone) 0/30
I entered the Tzenkethi Battlezone and the Hard Endeavor changed to 0/35. I thought nothing of it and destroyed some ships. Somewhere around the 10th ship, it indicated that I finished (both the textbox and the Endeavor box). I only received an Easy box.
I exited the TB and immediately, it popped up saying that I completed the Easy Endeavor. Now, the Easy Endeavor appears to be finished while the Hard Endeavor has returned to 0/30.