I can't open your flicker picture, would be better if you use Additional Options, Browse to your locally stored file, and Attach it.
You mention
why is there voltage after the P-Channel Mosfet when the gate voltage is brought high?
If the control signals to devices powered by that line are high, the voltage can leakt thru their input clamp diodes and power the device. If you plan to cut power, you should bring their IO lines first so that doesn't occur.