I've heard of this problem before as well. On my older 98 D there is no such thing as a brake shift interlock switch, but the key must be turned to allow the shifter to be moved down from park, other than that you don't have to depress the brake to move it, even when the engine is running.

Then again you have the 4.7 motor which means you have a whole different transmission that may have had a faulty park prawl or a different shifting mechanism that allows much easier shifting out of park.

Anyways do exactly as magic said and use the parking brake at all times...well of course not when you're driving haha.

 

there is a interlink. your d wont have one its to old its from like 2000 to 2003 and yes the 4.7 will be different thats why i said it was a 2002 with 4.7.