Investigating this in a bit more depth on one of my Jessie laptops, I note that if I switch the desktop session from Gnome Flashback to Gnome Classic (or, after installing it, Mate), then attempting to join a new wifi network does throw up the expected dialog prompting for a password, and generally seems to work as expected.
So seems to me the issue may be specific to Flashback. (For me, switching to Mate looks like a good solution in that it seems to tick all the boxes which were leading me to favour Flashback over the other Gnome options, but I may try and persist with Classic for a while longer). Tim -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org