It's called Ingress and bryans explanation of it is correct. The off air channels are getting into your cables and mixing with the cable signal. Ghosting will only occur on channels that can be received over the air.
Check for "push-on" jumpers. They are the number one cause of ingress. Make sure you have all the screw on types. Make sure all your connectors are tight. If all else fails, call you cable company. They have a "leak detector" that will take them right to the problem.
Also, some TV's have what's called "direct pickup" Which means the off air signal is coming right into the back of your TV. If this is the case, just use the tuner in your VCR, or add a cable box.
I am not sure how your cable company works, but ours has no charge for this as we have to do yearly FCC Mandated tests on our system looking for leakage or CLI. When we find it coming from a home, we fix it no charge
There is a chance, all be it a small one, that it is coming from the systems hardline. If this is the case, they should not charge you, but yet credit your account.
Hope this helps...