In the GZDoom SVN changelogs, I read this for GZD r1307/ZD r3426: Fixed: FMOD as MIDI device always looped the song, even when it shouldn't (such as the title music).
If the title music isn't supposed to loop, then I should mention that it still does with latest GZDoom release (r1318) at least. And I am using Timidity for music playback (which isn't even used since I use MP3 tracks). This is somewhat annoying since the game forces the title music to loop after the intro screen shows for the second time, interrupting/restarting your replacement music (in case it is longer than the original Doom title track, e.g. when using PSX title music). Any chance this gets changed?
I have tried both a midi and an mp3 as the title music and neither of them restarted when the titlepic was revisited. They just kept playing as I would expect. I tested both ZDoom and GZDoom. I have actually been using a long-ish mp3 as title music in a mod for years and never had the problem described with it.
I will try deleting my zdoom.ini file and see if that fixes it (wouldn't be the first time) - with latest ZDoom and GZDoom builds. However, I thought Timidity is only used when you are not using MP3 replacement files, so I assumed that can't be the cause. Anyway, will report back once I have tested.
*EDIT* Checked again with latest GZD r1322. MIDI tracks keep playing when intro screen pops up for a second time, OGG/MP3 replacements will be interrupted and start from the beginning. Deleting ini file didn't change anything.