Sounds like the "safety feature" built in is, um, very aggressive. It is supposed to lock down whenever it detects the ball pulling out downward, i.e. the hitch going up off the ball, as well as the ball pressing back on the shoe at the back of the latch. The trick that has always worked for me is to chock the trailer's wheels so it can't roll forward, then before making any attempt to jack up the trailer, putting the TV into forward gear and putting a bit of pull on the hitch. Leave it in gear, pulling at idle and get out. Flip the latch, it should open right up. The TV will not go anywhere because the full weight of the trailer is still on it. Climb back in, put 'er in park and set the brake, then jack the trailer off the ball.
Obviously, care needs to be taken here. If there is a WDH involved, it must be removed before any attempt is made to unlatch.