Game Mechanics: Melee intermediately stopping

[Itchybottom]

I saw this with an Erudite Emissary in Toxxulia (which got me killed) and now Faldor Hendrys twice in North Qeynos. I'll be in the middle of giving something a beat down with my rogue, and then auto-attack just stops. I see the mob flicker below z-axis and above z-axis every now and then. Backstab still works. If I turn off auto-attack and turn it back on, it does nothing to resolve the problem. In order to hit the NPC again, I have to move the NPC around until my attacks resume.