I have been converting my CD collection to FLAC. Along the way, I have been combining saving multiple disc sets (say Brahms' four symphonies) into a single folder. I'm using Exact Audio Copy which allows me to save the second CD with file numbers that continue from the number of the last track on the previous CD. So CD 1 has 12 tracks; then EAC numbers the first track on CD 2 as 13, and so forth. When I open the folder in mp3tag the files are all shown in the correct order. I then change the disc number to 1 for all tracks or leave it blank. I also renumber the track field to match the file numbers. However, when I upload the folder to my music server, the albums still show as separate CDs. Is there a metadata field that I cannot see in mp3tag that is causing this?
If you suspect a tag field, have you checked the extended tags dialogue Alt-T?
Grouping individual files together as one album is a feature of the player.
So it would be a good idea to cause the player to update any cache or database that it may maintain.
AFAIK the fields for ALBUMARTIST, ARTIST; ALBUM, TITLE should be filled