Mac 2015 User

When I change styles eg from swing to latin, or from latin to 12/8 ballad, BIAB re-writes the melody line with that feel, for example adding dotted hemi-demi-semi quavers. I am exaggerating slightly.
When playing Jazz this is not the convention I am used to and wonder if there is a way to stop the melody line from being re-styled.
I'm sure it didn't happen on my old Windows version?