Raiden stage music repeats after stg 3? hardware difference?

[kemical]

I was noticing that the stage 1 music plays on stage 4, stage 2 on 5, 3 on 6, etc.. is this common on all Raiden hardware? I seem to remember there being more varied music in the game. (I guess I could check in MAME)

[elbarto]

Going by the OST track list:
(couldn't remember offhand, haven't played far into the game in years)

Go to Blazes - Stages 1/4
Lightning War - Stages 2/7
Rough and Tumble - Stages 3/6
Fighting Thunder - Stages 5/8