It's pitching moment. The Bee's airfoils will have a strong nose-down moment.
At speed, this overcomes the down lift from the horizontal, and the plane tucks.
I've have some slopers that will do this on command.
Moving the c.g. forward helps.
The COX foam Bee had this "amusing" feature (feature in the MicroSoft definition).
Too much of a dive, and it tucked. And then the wingtips would meet on the top of the plane.