When you select unit or squad leader, and then set the way point to the building (way point with the red square, where you also specify position in the building). This way point becomes attached to the center of the building and makes it impossible to move it and also impossible to make another way point for the same building from another squad where it would also be nice to specify position...
Well, actually you can, but this way point will become spawned on top of previous one making the previous way point inaccessible without removing the one which was spawned on top of it