I suppose since your search has the same number of results with or without your parameter "&has=movieconnections", you're correct in assuming that parameter does not work. How did you decide on that syntax? I don't see Connections as one of the choices in Advanced Title Search. And parameters often don't cross over between IMDb searches (assuming you found it somewhere else).
Hi rootsmusic, I can confirm that movie connections is not currently available in the advanced search. However as a workaround for searching for Prequel titles, you're welcome to search using the "prequel" keyword.