Temporary camera positions using scenes is a good way to work.

The problem is that copying glued components from one face to the other requires you to pick a reference point wich MUST be on the original face.

COPY+PASTE uses the point with the minimum Z, X and Y of your component's bounding box as a reference point.

Sometimes that point is on the original face plane sometimes it's not.

So, when you paste it on the landing plane, sometimes it glues sometimes it doesn't.

Either follow what Dave says or simply use MOVE+CTRL to copy with an accurate reference point.