backing up trailer with/without lockout key?

I recently purchased an 02 X-star. This is my first boat that has brakes on the trailer. The previous owner told me I needed to install the lockout key when ever I back up to prevent the brakes from engaging and the trailer from bouncing. I forgot to do this the other night and the trailer seemed to back up as normal as in the past. I have an 04 2500HD Chevy and I have the 5 way adapter. When I go in reverse are the brakes being bypassed through that 5th wire? Or do I still need to be using that lock out key?