I created a Panel Theme based skin for my customers and uploaded my "Logo for Panel Theme" there.
I set my new skin as default under
Top > Configuration Director > Miscellaneous Settings > Interface Settings.
When I go https://OBAS ip address or hostname/cp I see my logo there.
But when I press "Forgot your password?" my logo is changed to a default one.
Software issue PBAS-29875 that was fixed in OBAS release 4.5.4.