MC 17.0.27, Windows 7 x64
When you have two of the same song in playing now, selecting it to play always jumps you to the first index of said mp3.
Steps:
Add 'x.mp3' to playing now
Add a whole bunch mores songs (so the viewport displays the scroll bar, and that x.mp3 is no longer visible in the viewport)
Add 'x.mp3' to playing now a second time (at the end of the queue)
Play the second 'x.mp3' by double clicking it.
If it was recreated correctly, the first 'x.mp3' in the playing now queue will gain focus (and zap you to the top of the playlist).
This doesn't look as designed since its a bit jarring and you lose your position.
Hope it helps!