I basically have the same problem as this guy had: http://community.monogame.net/t/song-cutting-off-prematurely/7742/21
Unfortunately there was no perfect solution found in his case.
In my case I load my song through the pipeline tool with Content.Load and use MediaPlayer.Play(song) to play it. The song's length as seen song.Duration.TotalSeconds correctly corresponds with the length of the audio file. However, the MediaPlayer stops around 1 second too early; you can hear it stop and the MediaPlayer.State is set to Stopped when this happens. The "solution" by adding an extra second of silence kind of works, but it is not exact, and looping or playing a new song doesn't flow smoothly.
I have tried both the mp3. format and the .ogg format. The song is played correctly in Windows Media Player. My project is a Monogame Cross Platform Desktop Project. Is this a known bug or is there some trick to it? I have seen several forum posts about it, but no solution.