Obviously that should not be happening. Don't know who you used to install, but It is hopefully a shop that will stand behind their work. I would give them a chance to make it right. I am frankly not familiar with the braking system you have, I use a U.S. Gear system, that uses the cars own power braking system, proportionally. It should IMO never apply the toad brakes with no braking going on in the towing vehicle. Possibly an equipment failure, but as I say, I'm not familiar with your system, so it could also be a setup issue.