during building, the normal vector of the player (as opposed to the normal vector of the surface on which the buildable is being placed) is used as the buildable's normal vector. due to the wrong vector, eggs can self-destruct when they wrongly find that the spawning area is blocked by the world. fortunately, this bug only shows itself when instant building is enabled; otherwise the normal vector of the buildable is shortly corrected (before the buildable is finished).
Created attachment 2777 [details] use the correct buildable normal vector when building G_CanBuild() now provides the surface's normal vector.