This is about the Update server behavior and the data type that you are submitting. On the page it is set to a double, but you want to submit a Date.
1) Open up the update server behavior
2) Select the date column that isn't updating properly
3) Choose "Date" from the Save As select list on the bottom of that page
4) Click OK to save your changes
5) Upload the page to your site
If you still have issues, please attach the actual .php page to your reply to this thread and I can open it with Dreamweaver directly. Please mention the column name you are looking at so I can be sure we are looking at the same thing.