Welcome to the forum
That does sound more like a firmware bug (software bug in the keyboard) than a fault with your sustain pedal. Unfortunately I don't have the mkII so I can't test at my end. Hopefully someone can chime-in with more experience.
Whether they do or they don't, it still might be worth opening a support ticket with Arturia. If it is a bug, opening a support ticket effectively raises it through the right channels.
Hope that helps.