the Store order summary and store order details are using the same trigger, it does not make any sense that the summary would not be stored, but the details would. if that where to happen, the details would have an empty value for the DetailOrderID column, it sounds more likely that the new order is overwriting an existing order.
make sure to clear the session on the success page, this could cause a new order to over write an existing order.
add the following code on the success page after the </html> tag to clear the session:
<%
Session.Abandon
Session.Contents.RemoveAll()
%>