the mosfet gate turnon voltage is always in respect to its source terminal. So when the source voltage is at 4.5v and the gate is still at 3.6 it could already start turning on (logic level mosfet too ? ), so you drop the gate voltage to turn it on hard, sure it might not turn off then, no mystery there :smile:
You must level shift the gate voltage to pull it down with respect to its source.
Use another transistor, npn, collector -resistor (say 1k) - mosfet gate + mosfet gate - resistor (say 100k) - mosfet source.