I have BiaB Audiophile 2021 version 840 on windows 10

I've muted two instruments for the intro then set them to play on the fourth bar. I've done this in Bar Settings. On play back, this all works as set and the two instruments are silent then play on the fourth bar.

However, When I drag and drop my tracks onto the master panel as wav files then play these back, all instruments play from the first bar including the instruments I had muted.

I'm sure that, in previous projects, this didn't happen and that muted instruments were also muted in drag and drop files.

I'd be grateful for any help with this.

Thanks.