When I try to open a backup file with the .vlb extension it opens a blank callmenames file. Looking at the underlying xml, it is identical to the normal .vl file in the sketches folder. And indeed, when I switch the backup file from .vlb to .vl it opens normally again.
Happens with the latest version (252).
Edit: Opening the file from within vvvv gamma using Ctrl+O does work, though.