If your song is 3 choruses or longer, the middle choruses will play B substyle regardless of part markers. You can turn this off in Song Settings - Vary style in Middle chorus. I've had a few multiple chorus (unfolded) songs where the 2 bar ending sometimes played the B substyle even though it was marked A. I believe it was one of the Bossa Perc drums kits.

If you really want to get to the bottom of the issue, turn on Developer Mode in RealDrums Settings. The lines may be somewhat cryptic but you will see if it is really generating B drums. The line will show the Bar # and if it is a A or B. Here are a few excepts from a song using Jazz drums.

Note the Bar# and the 'Normal,a' or 'Normal,b' parts.

Bar# 18,relbar=6, MaxBars=3, Chose pat#32, line #38 Normal,a sub.,mask=0,dur#bars=2...
Bar# 44,relbar=8, MaxBars=8, Chose pat#78, line #84 Normal,b sub.,mask=2,dur#bars=4...

HTH

R