[samibe]

My surface does this too. Although mine does it for all tabs that have secondary lists (Collections, Albums, Artists, etc. and even Years). 

If I select a tab and pick an item that has several songs in it, then long pressing on letters brings up secondary letters that aren't on the list. Also clicking on the secondary letters doesn't move the list down to that area in the list. Clicking the primary letters does though. 
It's very obvious when one of the letters only has one song in it. There are usually multiple secondary letters and often the second letter in the song title isn't one of the secondary letters.

Turning on "Show Extended Letter List with Tap" in the settings seems to switch everything so that it works correctly, though.