UpdateRequest SuppressDuplicateDetection parameter does not work.

I am trying to update the account associated to a new Opportunity I am creating. I wrote a plugin to retrieve the account, update a field and then update the record. Problem is I get this error:

A record was not created or updated because a duplicate of the current record already exists.

It's being caused by the fact that I have a duplicate detection rule that sees another account that may be  duplicate of the one I'm trying to update. So I found this parameter I could set on the UpdateRequest object to make it ignore duplicate detection called SuppressDuplicateDetection. Problem is even if I set it to true I still get the error. Here is the code I am using.

                            UpdateRequest reqUpdate = new UpdateRequest();
                            reqUpdate.Target = accountEntity;
                            if (reqUpdate.Parameters.Contains("SuppressDuplicateDetection")) 
                                reqUpdate.Parameters["SuppressDuplicateDetection"] = true;
                            else
                                reqUpdate.Parameters.Add("SuppressDuplicateDetection", true);
                            UpdateResponse updateReponse = (UpdateResponse)service.Execute(reqUpdate);

Based on my testing I can only assume that this parameter does not work. Has anyone else used this with any success?