Watchers/guards like to stand all the way into doorways and block them, this happened at Candlekeep Inn and the Barracks. Sometimes this means a PC can't enter the building then and there's no way of getting the blocker out of there.
Maybe the NPC is actually trying to enter the building and nothing happens... hard to say.
No, it is a pathfinding problem. The original forced the actors to slide away.
This is indeed a pathfinding 'bug'. Or rather, a missing feature.
The bumping of friendly actors is not yet implemented.
As this is a missing feature, not generally breaking playability, it is low priority.
BG1 had no bumping, and scripts in BG1 seem to generally only walk to doorways in order to move areas or destroy themselves, so I think sprotte probably has the right idea here.