Disengaged or not

[Jack_Wick]

A right-handed pitcher makes a feint toward second base. While doing so, he lifts his pivot foot off the rubber to gain momentum, but then his pivot foot lands on the rubber again. Would he be considered disengaged or not?

 

PS. Which rule allows you to disengage simply by lifting your foot off the rubber? (I mean without having to step the pivot foot behind the rubber)

Thanks everyone.