Login button greys out when I change SSO server

On some clients I’‘ve noticed that when clicking SSO, the server setting will auto-populate, but if I try to change anything (username or server) then the login box will grey out and I can’'t click… but only on some machines. On other machines I can change username and server settings and still click login.

It doesn’‘t matter what settings I check/uncheck… I’'ve tried checking/unchecking auto-login and auto discover host/port.