Spells: Mask of the Hunter bug. Disappears from buff bar, reappears on zone/relog

[Bummey]

I've been having a problem with the druid spell Mask of the Hunter lately. Sometimes after a short time the buff will disappear from my buff bar, long before the 3 hour duration is even on the horizon. I thought it was getting dispelled by Tserrina or one of the enraged vampires. I'd lose see invis and mana regen would slow ever so slightly, but when I zoned out to recast (or relog) it would reappear on my buff bar.

Uhhh that's it. Dunno what more to say. After a period much shorter than the duration of the buff it disappears from my buff bar and and reppears when I zone or relog. So far it's only been happening in Tower of Frozen Shadow, but that's also the only place I've played my druid for extended periods without zoning for like the past month. Perhaps it has something to do with its ridiculous duration, something that wouldn't be noticed with shorter duration buffs?