R.E.N. Spells Ren
Veteran
No, it's iTunes fault. When you tag a song in iTunes it doesn't save the tagging to the mp3. It saves it to a separate database. That's been a known problem with iTunes. Use tag&rename to do your mp3 tags if you're planning on using non apple devices. It stores the tags to the mp3 so regardless of what player you use, the tags will show properly.
Then why would Google Music on the browser correctly order the tracks while the Google Music app on my phone plays it out of order?