When changing Styles mid song, the names of the tracks in the Mixer will visually remain the same as how they are written in the first Style. But you will hear them change with the change of Style during playback. Currently this is how it is designed, so technically not a bug. However it may be good to add this to the Wishlist forums for future consideration.
https://www.pgmusic.com/forums/ubbthreads.php?ubb=cfrm&c=3


Best,
Chantelle