Plane Primitive Turned into Sphere

Escribano

I created a simple plane primitive with five divisions to use as a floor surface. I added some d-Formers to reshape it into a trapezoid, saved that as a morph, then applied a texture. I created seven instances of the primitive. Then I went on to work on other stuff.

When I opened the scene file again later, I discovered that the plane had turned into a sphere. The morph that I made is still on it, but doesn't do anything since the object is now a sphere and not a plane. The scale sliders are all in the correct, positive values.

Can anyone tell me what happened? Before I try to recreate the plane as I had it before, I would like to make sure this one doesn't turn into a sphere again.