It's a mess. When you restore session, it DOES NOT restore the session, but ADDS windows and tabs to the currently open ones.

Suppose you have 10 windows and saved the session. Then later on you navigated to some other URLs. Now you want to restore the saved session. But after you click on restore, current windows will NOT be closed, but new windows will be added. Now instead of 10 windows you have 20. If you activated autosave and restore a newer version later on, you will have 40 windows, then 80, then 160, etc. Each windows will be duplicated 4, 8, 16 times etc.

I don't see any option to disable this awkward mode.

Having this awkward mode makes the extension unusable.