I had the same problem late in the fall in temps in the upper 20's. I always just launched my boat and used the Ulterra to bring it back to the dock after I parked my truck. That morning it just floated away across the bay and a friend had to go and retrieve my boat for me.
Anyway the problem is on the lubrication of the latch pins and the ramps. Lube them up a little, I used teflon dry lube spay and have not had any issues since. By the way that only happened to me a couple of times, always in really cold weather, When my boat drifted away was while we were launching for a tournament and a bunch of my friends around to laugh at me, but at least they were there to go and get my boat for me.