From Kurzweil manual -
In the K1000 keyboard instrument, Note Off’s are transmitted using the MIDI Note Off message $8x kkk vvv.
This can cause problems with certain simple minded MIDI processors (such as the Yamaha MEP4) which transpose
the MIDI stream by only altering key numbers in Note On messages ($9x) on the assumption that the MIDI controller
is sending Note Off’s as zero velocity Note On’s. Currently, there is no solution to this problem but future versions
of the software will add a master parameter to select the type of Note Off (real Note Off or zero velocity Note
On) which is transmitted.

source - http://www.synthzone.com/midi/kurzweil/k1000/K1Ksysex.pdf

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