I had this problem. But this week updated to 188.8.131.52.gb388fe17 and it seems to be working like it did originally (i.e. as long as you sort in the same order as when you started playing the playlist it finds the correct track - but occasionally off a bit if you have been adding/deleting tracks since starting to play.)
Strange because I have exactly the same version and OS as musicpet who seems to still have the problem. Maybe musicpet you should try what I did - go back to an old version and then reinstall the new one?!
In my playlist it seems to skip the order of the songs by the amount of "unavailable" songs backwards (the songs that are dark and you can't play them anymore but they are still in your list) that are in the list BEFORE the played song (counting from top to bottom of the list).
Meaning: Current playing song order = x Amount of unavailable songs before x = y
When clicking on current played song it will display: x - y = z order of song (from top to bottom).
Example with pictures:
Let's play this song here called "Misery'n" in this playlist, I have only 2 unavailable songs in this playlist and put them close together so you see them at once: Now I click on the album art and as you can see it skips the original songs order -2, as expected since the 2 unavailable songs come before "Misery'n" and marks "All the things you are" Now let's play another song, this time after one of the unavailable songs: Now when I click on the cover art of "All the things you are" it skips to the original songs order -1 because only one of the unavailable songs comes before this one. Now let's play one song that is after both unavailable songs: Now when I click on the cover art it doesn't skip any order and shows the correct song, because this song comes after both unavailable songs:
Sorry if anyone already mentioned this, I don't have the time to look through all comments, hope this helps, gotta go again!