from the first post, it sounds to me like the OP is trusting the keyed cable hanger to keep the adjustable cup from turning when tightening the locknut. and is NOT holding the cup with anything at all. and assumes that just tightening the locknut onto the keyed cable hanger will be sufficient. as i mentioned, i'm not so sure it is.

i have done this in the past with a keyed washer instead of a cable hanger and was disappointed with the results.

a pic would be nice.