Looking at this further: I had the exe's mixed up - the proxy UI was getting .exe added in ubuntu_sso/__init__ -- the two that weren't were the 'ubuntu-sso-login' backend, which had been found using the registry, and the ubuntu-sso-ssl-certificate-qt UI, which would have the problem I outlined above.
As far as I can tell from a few minutes reading through the code, that UI won't be called correctly.
Looking at this further: I had the exe's mixed up - the proxy UI was getting .exe added in ubuntu_sso/__init__ -- the two that weren't were the 'ubuntu-sso-login' backend, which had been found using the registry, and the ubuntu- sso-ssl- certificate- qt UI, which would have the problem I outlined above.
As far as I can tell from a few minutes reading through the code, that UI won't be called correctly.