Hmmmm. I just checked it but there is no filter in the OTS Hold menu for the split control. There is in performance hold, but with that set either way, my BK7m doesn't change the split setting by selecting another OTS on the panel. I suggest you check your firmware version and ensure you are running v1.05. I don't remeber having a problem like this on v1.04 but I may have missed it.
John
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Roland G-70, FP-4, BK-7m, SonicCell, KC-350 x 2, DS-5 x 2, A300-Pro, Sonar X1 PE, BR1600CD
Yamaha HX-1 System 1, KA-20x2