Back during Patch 5.4, I looted the Heroic variant which then became the Mythic variant of the War Staff, however with the MoP Remix giving the ability to buy the old Normal version that beccame current Heroic version, it seems that ATT does not correctly account for higher variants than those currently purchasable on MoP Remix.

From the screenshot, my War Staff was already 4/4, I have tried the usual hard refresh, relog thing and all that without luck.

When I hover the item listed in ATT > Character > Heirlooms > Weathered Heirloom Scabbard, I can see that Hellscream's War Staff is listed as the Heroic version too, leading me to believe it is not a caching issue.

I'm having the same issue but with Hellscream's Warmace