Muzz, just keep in mind if the cord is ancored to close to the rest it 'will' haul the rest down with it after the shot also.
When I first started using this rest, four years ago, the same thing happened and I tightened the rest using loctite on the bolts. The thing moved a week or so after. Couldn't understand. Then I moved the trigger cord further down the cable, tweaked a bit and the rest stayed in position ever since.
Be careful if the rest does this again, as after speaking the Cabe @ Spot Hogg, this is one of the causes of the trigger breaking the internal spring. The spring is replaceable...but you wouldn't want that to happen.
Lengthen the cord a bit. If your cord is already too short, use some BCY #24 d-loop material, it works just as well.