Cig Lighter Draws power even with ignition off?

Odd thing just happened to me. S/O and I went to the local Cracker Barrel for dinner. Just as we get there to park, she pushed in the cig. lighter, but it didn't pop out before I parked and shut the ignition off. 2 hours later, the battery was stone dead - needed a jump to get going.

It ran fine afterwards, the DIC showed 13.7 - 14.1 volts going in to the battery.

This happened once before when I left my cell phone charger in the cig lighter overnight.

Is this SOP for the lighter to stay "hot" even with the ignition off?