why are our Producer names changing on their own?

We have noticed that some of our shows producer fields are incorrect, as if the system is changing them. When we search for a show and the list appears some of the producers are wrong (but are the same wrong producer) yet there is no way that an operator was to blame for the error. One reason being that an old show will be showing a producer that wasn't in the system at the time that the show was last accessed.

It tends to be older shows that are affected. Any idea why this is happening and whether there is a solution?