Can a capacitor in a circuit receiving no power regrow a charge?
In an ideal capacitor, the dielectric is a perfect insulator and is not affected by nor affects the charge on the plates. In a real capacitor, this is not true.

What can happen is that during operation the dielectric can actually absorb some of the charge from the plates. Once the charge has been drained from the plates externally the dielectric will release this charge back onto the plates. Naturally this re-energizes the capacitors, potentially to dangerous levels.