[amsat-bb] SAT PC 32 AND YAESU FT-847

If I turn the vfo knob on the ft847 too fast , it will change modes from lsb to usb on the radio.if I turn off cat cotrol And turn it on again it cures the problem. I have two ft 847 radios,it have tried both of them with the same results. What am I doing wrong ? Jeff WB8RJY