It seems like nothing changed, and the system is working as designed. If the only resolution you had selected was 1080p, then that is the only resolution the box will allow. But since most content is not 1080p, non-1080p content will default to 480, apparently.
Remember that 1080p as a delivery format and 1080p as a native screen format are really two different things. 1080p the delivery format, at least for consumers, implies a source frame rate of 24. 1080p as a screen display format is only telling us that the native pixel map is 1920x1080 (the map everything else must be scaled to) and that the display is progressive in nature (implying that it deinterlaces all interlaced content). It also implies a native frame or field rate of 60 fps (actually 59.94), and many sets are locked to that rate implying the need for 3:2 pulldown with 1080p24 content. More sophisticated TVs can scan at multiples of 24, and so do not need pulldown.
Even HD or SD video telecined from 24 fps content and delivered as 1080i30 or 720p60 is actually transmitted as 24 fps, surprisingly enough, and pulldown recreates the missing frames locally at the STB by duplicating the transmitted frames, x3 for even fields and x2 for odd fields, unless the TV is equipped to scan in multiples of 24, such as 72, 120, 240, or 480. That is referred to as "film mode", and is done to take advantage of the efficiency of not transmitting duplicated frames.