Cannot connect to open network with captive portal

[Alan Pope 🍺🐧🐱 🦄]

Visit a location with an open wireless network which requires you to click "agree" or similar before connecting to the internet proper - a so-called captive portal.
Using system image 5 on mako I am unable to make such a connection.
I can see the network, click on it in the network-indicator, but I don't get an IP address, and no way to visit the "agree" page.
I can connect to other open (and secure) networks just fine, and other devices can connect to the problem network (but prompt to "agree" in a browser).

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[taiebot65 (dedreuil)]

A workaround is to open a webapp like bbc news and you should be re-directed to the captive portal. (anyway that's what i am doing)

[Matthew Paul Thomas (mpt)]

Alan, if you open an http: URL (for example, <http://example.com/>) in the Browser app, do you then get the page where you can click the button? If so, this is a duplicate of bug 914507.

If not, what happens when you try?