NPCs can be pushed by players

[Tauryuu]

When they got moved, their location are saved and you'll have to reset them to your desired location.

I tried to set up waypoints so they always moved back to it, but it doesn't work 90% of the times.

[ghost]

Bukkit #1000
Citizens 1.0.9d

Same issue, but only on "half" blocks (i.e. step blocks & lower half of stairs).

[MinecraftAdmin]

I am having the same issue, but on full blocks.