The Bell 412CF used to have a similar problem on every aircraft that was corrected by a software upgrade to the TARSYN if I recall. The problem went away even if only one of the Tarsyns had the updated software. The yaw kick was only a couple of degrees though when decelerating through about 60 kts, you make it sound like this is a new thing in your aircraft and more significant then a few degs of yaw. Might be worth checking if you've recently swapped one out and perhaps have an older software version now.