I have set up commerce extra / autopopulate correctly and everything works fine when I have my 'billing info' pane enabled. However when I set it to disabled, the billing info doesn't get filled out.

This is probably by design. I just thought this might be possible (the info is already auto-populated, so why bother people with the extra clutter on-screen).

I think I might be missing something in the flow, please enlighten me.