It also happens for alpha mode (yay!), i want to have a bug for this for tracking purposes.
The login page of MobileFrontend actually is provided by it's own implementation to fit the needs of mobile devices. It isn't really needed anymore, the login page customisations should be done with special css rules or in core. Actually it's difficult to overwrite the loginpage for other extensions (like GoogleLogin), if MobileFrontend loads after this extension.