datepicker plus (+) and minus (-) keys not working

datepicker plus (+) and minus (-) keys not working

so I have initialized text fields with a certain class to get the datepicker, the problem is once the user has clicked on the date field if they start typing in the field they cannot type a plus (+) or minus (-) key into the field. I'm sure there is any easy fix for this that I have missed if anyone can help me it would be greatly appreciated.