The only way it would happen is if you have a stack of your pawn and
an opponent's piece on top, and then you place your drone on top of
this stack! The correct course of action, in such a position would be
to spend the one point to dig your pawn up first, and then move the
drone on top.
Actually I've found that this is usually a result of a defensive
move. Medium Yellow Mid (as per previous examples) stays on the
Blue Center and continually digs to the top to "get between" Blue
mids.
I'm often just trying to get all my Blue 'Mids onto my coaster - and
then into the center - I'll worry about stacking order later if I have
to.
:)
Carol