When I disable SessionRestore and then re-enable it, it closes all existing tabs in all of Safari's windows and opens a window for SessionRestore.  I then have to invoke SR to restore all the tabs and this may take a while if I have several windows with a bunch of tabs in each.

Is this by design?  I sometimes need to disable all extensions to test if one of them is causing a strange behavior on a particular website.  Having to wait to reload all the pages is annoying.