I have recently contacted ms about this issue, they replied that the next version of xbox music will fix this issue. I won'be able to test it since I succesfully reverted back to 8.0 lumia black which also fixes this issue. And several others as well. Music +Videos hub is super fast, the entire os is much more fluid.
Anyway, if the update comes would you guys be interested in checking the glitch with two test files I provide?