It is definitely not a bug, you shouldnt be spamming the IWT key faster than the pathing mechanism can resolve itself and you need to know that your IWT pathing is for the location of the mob when you pressed it, not for where the mob is currently.

What your characters are clearly doing is orientating or reorientating themselves to a moving target and creating a path to that facing. This never happens on stationary targets (like a dummy, an stationary npc, or various very slow moving mobs) no matter how much you spam the IWT key.

When a character runs off into the distance is likely that the camera changed or the mob became unavailable to be interacted with and you technically forced the character to click move to a point off on the game terrain. This movement is directly akin to the repathing delay queue. Also interrupting the IWT queuing can cause the click point to not be the target but some line in the pathing route.

Since the pathing routes are very complex (if you watch a hunter pet path for example its quite ingenius how the move around all things considered) you are likely in for some surprises when your character aligns to one of these orientation lines.