Searching by date field created with 'now()'

I have a table with a "Date Changed" field in it, which is set to automatically update every time the record is edited by using "now()" in the Edit Format and making the field a hidden field.
When a user attempts to search by this date using the "contains," "equals" or "starts with" operators, it yields nothing if they enter in the entire date. If, however, they use "more than," or "equal to or more than," it finds all the records. If they use "Starts with" and enter the month and day with two slashes (e.g., "10/16/"), it finds all the records, but not if they use the full date (e.g., "10/16/2005"). Am I doing something wrong here?
Thanks,
FG