Since Sync feature was introduced for this add-on the container flag no longer comes back with session restore.

When I use containers that were created some time ago, tabs re-open in those containers, correctly.

When I create new containers these tabs open in normal tabs when the session is trestored, so the container flag is lost for them.

Whatever may be the difference between older and newer containers - since the sync feature was added this behaviour is happening, rendering the add-on useless in my case.