Wrkinit, you should not have to use the clear styles button in order to change styles at a bar. I have tried to reproduce your problem on BiaB 2011, and was not able to. I added styles one-at-a-time and played through the song to make sure I heard the difference each time in each chorus. It worked fine with 5 styles and 3 choruses. I also succeeded in testing clearing several of the styles changes I made, and the changes were heard consistently in each chorus. All I can say is that it works for me in BiaB 2011.

Other thoughts:
Are you stopping the playback and using the play button to make sure that the new styles get generated? I think I remember changing styles once and the new style not taking effect until I did that. (But usually it takes effect right away.)

If you are using repeats, dal Segno, or da Capo instead of just BiaB choruses then a change in one chorus does not get copied to the other choruses. If you are only using the usual BiaB choruses then changes in style or chords in one chorus do get copied to the other choruses. (Melodies, however, can be different in each chorus.)