Tested wanted!
I managed to create a Whonix stable upgrade. anon-ws-disable-stacked-tor version 3:2.3-1 is now available from Whonix jessie-proposed-updates and testers apt repository.
Once you updated that package and rebooted, Tor Browser version 6.5a4 will have fixed connectivity. Please test!
(Whether you run sudo apt-get autoremove after upgrade to get rid of rinetd [previously used to implement anon-ws-disable-stacked-tor doesn’t matter since it will be doing nothing but waste a very little memory if it stays.)