Reverse voltage flowing from drain to source in P channel MOSFET
In each MOSFET, the body forms diodes with the drain and source junctions. The body in a pMOSFET is n-type, while the drain and source p-type. The opposite in in an nMOSFET.

Discrete MOSFETs have the body and source terminal shorted together. This form a diode between source and drain. To see the direction of the diode, just have a look at the arrow in the symbol (in your schematics, the diode is also explicitly shown). On a pMOSFET, the anode is at the drain, the cathode at the source. The opposite occurs on nMOSFET.

Therefore, in your circuit, current will flow from drain to source, regardless if the pMOSFET is ON or OFF.

To avoid this, you can use a back to back MOSFET connection shown below.







simulate this circuit &ndash; Schematic created using CircuitLab