it depends on what MIDI message is the keyboard sending out to qtractor when you hit "play sequence"... if could be MMC-Play or MIDI-Start (SPP) or even something else you may possibly have mapped to the menu Transport/Play command...
you can switch off either or both of the first in View > Options... > MIDI > Control > MMC or SPP set to "None" or "Output";
or you can turn on the Dedicated MIDI control input/output option and NOT connect your MIDI keyboard controller to of the "control" input port that will be created accordingly;
for the latter case, you'll need to go Help > Shortcuts and reset the MIDI controller setting to the Transport/Play menu action, if any.
it depends on what MIDI message is the keyboard sending out to qtractor when you hit "play sequence"... if could be MMC-Play or MIDI-Start (SPP) or even something else you may possibly have mapped to the menu Transport/Play command...
you can switch off either or both of the first in View > Options... > MIDI > Control > MMC or SPP set to "None" or "Output";
or you can turn on the Dedicated MIDI control input/output option and NOT connect your MIDI keyboard controller to of the "control" input port that will be created accordingly;
for the latter case, you'll need to go Help > Shortcuts and reset the MIDI controller setting to the Transport/Play menu action, if any.
hth.
cheers