Custom Web Part

I created a custom chart web part.  The user can enter a start and end date to change the date range reported by the chart.  Those fields are validated and required. 

BUT, now we have added other web parts to the page.  Every time we want to change or add web parts the page will NOT save unless those start and end dates are filled in.  Why are those items not ignored in design/edit mode?  How do I get them to be ignored when I'm in design/edit mode on the page? 

Thanks.