The only style substitution I know of is when a checkbox in RT Settings that will swap a RT style for a Midi style. I think the list is very small - the last time I checked it works mostly for the original ZZ styles.

There is a Song Setting to allow RT substitution according to tempo. You may check to see if that is unchecked. I believe it overrides the global RT Settings to allow a particular song to use a specified RT regardless of tempo. Perhaps this is what is happening.

Does the problem happen in other songs or limited to one song?

R