Is this a bug?

[Jetshrike]

Ok if you are using a range attack on a enemy and if they go for long enough without hitting you or they are chasing tou or something similar to that, they occasionnly turn around become impossible to hit and when they reach where they were origanly they regain all their health and start attacking you again.

[Reaper]

That can get really frustrating :/

[Jetshrike]

It doesn't seem to happen to 'boss' like characters. i had one follow me for ages. Fortunetly I beat it before it beat me XD