Guild Wars 2

If you don’t have mastery points to spend and you have fully trained levels in everything, ie gliding, itzel, exaulted, nuhoch; you can no longer gain xp.

And when you get enough mastery points to clear one of the levels you trained, you will loose all your xp on your bar and not gain a mastery from xp.

So don’t let yourself gain more xp than mastery points. it seems those are more important.

Not a bug, I think, but design. I naively posted a similar complaint about Tyrian masteries in the bug forum but a couple of players kindly pointed out that it was probably working as Anet intended. You can bank xp only up until the point where your bars are full and no more.