This applies to the MiniNova
This is likely because your Footswitch Setting is set to “N. Closed”, which will turn the Sustain On unless you have a pedal connected and pressed down.
On your MiniNova, go to Menu > Global > Footswitch > Turn the Data Knob to “Auto”. This will turn Global Sustain Off until you connect a Footswitch to the Sustain Port and Active.