SSL selection interface doesn't work

When I choose Encryption: enabled (or required), I don't get prompted with the certificate selection menu. Either it's because the AJAX thing takes forever (although I don't see my cursor switch to a clock to indicate a pending request) or because it's just not issuing the request. Then of course when I submit the form it complains:

The encryption key field is required to enable us to generate a new SSL certificate for your site.

So this may be related with #955854: Site form can be very slow with huge number of platforms and packages...