Why is itunes placing my songs out of order (iPad)

I had previously bought the song “Wish You Were Here” by Pink Floyd and recently I bought the rest of the album. When I went to play the album, I noticed “Wish You Were Here” was placed after “Shine On You Crazy Diamond Pts 1-6” even though “Wish You Were Here” still had the number 4 next to it, it was placed after the song that had the number 5 next to it. I wasn’t shocked at this because it had happened with many of my other albums, it takes the most listened to song and puts it at the bottom (Muse’s ‘Uprising’ for example still had the number 1 next to it, but was placed after song 11). It got worse when all of a sudden, I was listening to Wish You Where Here [the album] and I pressed on “Welcome To The Machine“ which is song 2, it then jumped in between “Shine On You Crazy Diamond Pts 1-6” and “Wish You Were Here”, then I pressed on “Have a Cigar” (song 3) which then also jumped to the bottom, now the album has the songs in this order: 1,5,2,3,4

The numbers still say 1,5,2,3,4 on the side, why is this happening, it is very annoying...