Added AudioFormat to indexTags, but still seeing >>Complete Album on multi-disc album

[ptha]

I'm running MinimServer 0.8.4 update 97, on a Synology DS213, and browsing via BubbleUPnP 2.8.7 on my Nexus 5.

My music collection contains FLAC and MP3 files often for the same album (depending on where I'll be playing it) so I've updated my indexTags property to:
Artist, Date, Genre, #AudioFormat:Format, All Artists, Composer, Conductor, Orchestra

Then in BubbleUPnP I can navigate to: Artist -> Format -> FLAC -> Album
or: Artist -> Format -> MP3 -> Album as necessary.

This seems to work fine most of the time, but for some multi-disc albums, of which I have MP3 and FLAC versions, when I select FLAC or MP3 I don't see the Album, instead I see >> Complete Album then a list of tracks, it doesn't seem to group the tracks together in BubbleUPnP and doesn't show the usual Album Header (with album art, total time etc.) and so I can't select all the tracks at once to add to a playlist with the + button.

I've tried retagging, removing extraneous tags, but I'm not sure what the issue is. Any help would be appreciated.