Deleted all but one shape key: mesh still renders as (deleted) base?!

I’m completely baffled.

I shaped a flat plane with a cloth simulation, baked the frame I wanted into a shape key, then deleted the base- leaving only the new shape key. I thought this would force Blender to use the key the new base- and it looks correct in the viewport render- but when I render with F12, the mesh shows up as an unshaped plane.

Am I missing something obvious? Anyone give me a hint about what’s going on here?