Linq to SQL insert SqlDateTime overflow

In my new e-commerce site, I am using Linq to SQL.  In all my tables I have modfiedOn and createdOn datetime columns.  When clicking on my "add to cart" button, I want to insert the items into my OrderItem table, but I kept on getting "SqlDateTime overflow.  Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM.  These are set to automatically get the current utc date in my database upon insert like they've always been in the past, so I didn't see a problem.   But when stepping through my code, I noticed that these are set to a low value date of 1/1/0001 and sent into the database that way.   Ok, starting to make sense, so I set these dates myself through code and it worked, but why should I have to do that?

I played around with the "dbml" designer and found a property called "Auto Generated Value".  The description sounded just like what I wanted, "Value is auto-generated in database on insert".  Perfect, so I set both of these properties to true, recompiled, and problem solved.