Doo-Sabin subdivision requires collect_garbage

[stla]

Hello,

I've tried the subdivision methods. With DooSabin_subdivision, I have to call mesh.collect_garbage(), otherwise there are some faces referencing unexisting vertices. Is it normal? I don't see this collect_garbage in the example given in the doc.

By the way the Loop subdivision applied to my favorite Hopf torus gives an awesome result: