Queries :: Filtering Criteria Using Unbound Text Box

I have some filtering criteria in a query that is based on some unbound text boxes in a form. These text boxes contain start and end dates. This form is not based on any table or query. All controls are unbound.

The query functions properly initially, however, I am programmatically changing the values of the unbound text boxes in the form that are used by the query. After their values have changed, the query doesn't seem to recognize the change and therefore returns no values.If I manually change the the values in the text boxes and run the query it works fine. However, I would like to avoid doing it this way, if at all possible.

After programmatically changing the values of the unbound text boxes, I tried setting the focus to the text boxes, setting the focus to other controls, refreshing the form, requering the form, requerying the text box, so forth and so on.