This is still a bug. After beating on a mob for extended periods of time, agro seems to be truncated or whatever and lost by the tank, who has insanely higher agro realistically than those they lose it to randomly after fighting the same mob for a long period of time.
Yes this happens. When I'm passively combat testing for a long time, eventually mobs will drop aggro and wander away after a while (30+ minutes). I'm not generating more aggro (overflow) other then being hit in some cases so it seems like they just give up (mem blur). Quite sensible of them.
I've seen this happen on long duration fights and even on shorter times. More so with the shorter times it sometimes looks like a graphic bug where it will show me at 1 and show someone else as the target's target in the target box on the bottom right. Meanwhile the actual target of target will still show my toon who is tanking it. Only solution I have for cadira is to do shei quicker than 45 minutes =p
If you aren't taking actions against the npc it will memblur after 10 minutes. Pretty sure that's different from what this thread is about.
I've seen this happen with pets (they'll just lose interest in fighting and you have to resend them) but do not recall seeing it with PCs.