At present when looking at a multi-disc album there is no way to see which disc the track belongs to. For instance, here Buck Rogers Season 1 is made up of 3 discs however all the tracks are shown together as one long list (yes with track number restarting at 1 when swapping discs, however it isn't clear that the discs are in order).
There should be a section break & disc number between each disc's tracks to indicate that its a new disc.
Related, the disc of the currently selected track isn't shown in the "Selected" pane, even when defined in the tags.
I checked two multi-disc albums with MM5 and while the property is set, it isn't appearing in that pane. (Edited post to add alternative screenshots that fit the webpage, left links to originals) 
