By default, holding down ALT while dragging a note will create a copy.
I have never heard of a copy happening when resizing, which leads me to believe the following…
Perhaps there are two duplicate notes in the MIDI part to begin with. When you move one the other is exposed giving the appearance of a duplicate.
This can happen if your keyboard controller is sending MIDI on multiple ports and you have “All MIDI Inputs” selected for the track.
A quick test…
If you move a note, and then move it again, is it still “duplicated”
J.L.
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