In addition to what Bill suggests, this is indeed a known issue and has been recorded as a bug to be fixed in next releases. Contact support anyway should the have created a customer patch and they can advice you on how to download and install it, if any.
The work around for the time being is to use a variable instead of a field in the calendar object. That way the calendar will show all dates from minimum value to maximum value as specified in the object properties, while when a field is used, you can only select and browse the current date. Of course, you will need to change your expressions based on that field to use a variable, but that will work as well with no loss of performance.