I myself haven't run into this issue. First thing I would check that the black post is connected to the outer rail of your layout, or the black post of your transformer.
Do you have any other Legacy items in your collection? If you do, check to see if the same problem is happening with your other Legacy items as well. Since that will be a big help in troubleshooting the problem.
If you are having the same symptoms with your other Legacy items and the black post checks out. It could be down to poor connections on your layout or your Legacy system has a problem.
Best of luck to you!