I am not sure if this is a bug or if this was intentional and, thus, should be a feature request. I am erring with the latter.
When shares are locked, it prevents the original poster's own ability to share. I feel like self-sharing should still be enabled even when shares are locked for all other cohost users.
I know that I can easily toggle it back and forth, but for pages (projects?) with a single authorized user, I feel like a preferable workflow is allowing self-shares.