Small house building bugg/mistake?

So this is a rather small thing but it's been a slight annoyance to me for such a long time that i should probably try find a solution for it and google hasn't helped me so far.

So my problem is: A lot of the times in the beginning when i send the 3 starting vills to build the 2 houses the foundation gets placed, they walk up to the foundation and then...do nothing. Obviously since it's the start of the game the foundations are usually not really blocked by anything (only on one side by the other house if at all- but that would still leave 3 sides open) yet it consistently happebs that i tell then to build houses, go manage the scout,sheep queue a villager in the tc and look around the map (for example in team games where everybody was placed) and come back to find that my villagers have just been standing there doing nothing which then usually results in a little bit of idle TC from the very start. (Either housed or if i notice it very late also sometimes delayed sheep gathering leads to not having enough food for a vill for a few seconds a little later in dark age). Is that a known bug or am i missing an intentional mechanic about building placement that would explain this?

Any well known reason and possible solution or do i just have to focus on them until i actually see them start building?