This issue is being caused by Genie again trying to be helpful. Genie has been programmed to check the Title that is entered for a patient and use that title to determine a patient's gender. This is usually great for patients who have Ms, Mr, Mrs etc because Genie can correctly identify the gender from these titles.
Entering Mstr though confuses Genie - the Ms combination makes Genie assume you are referring to a female. In order to correctly have the gender calculated you should enter the full title of Master. Genie is able to identify Master as male and will update the record accordingly.