I ran into a similar problem recently, and it has to do with what data type your field is set to accept. If it is saved of a type date(), then it's going to be in mySQL's pre-defined format. So, what I did was....
Created a table with a field named DATE varchar(.
//in my page
$date = date("m-d-y"); //gets the system date and puts it in a string "mm-dd-yy" rtfm
<input type="hidden" name="date1" value="<? echo $date;?>" maxlength="8">
//hidden form element which stores the date
When the form is submitted, have it insert that value into your DATE field. Read the manual on date() to see how to get the exact format you want. I recommend the one above because you can sort by date if you so desire. Anywhoo, I hope I understood the problem and helped.