Have been trying to figure out why this happens. We have a shop that runs Magento 1.9, that doesn't use the built-in customer account/sign in functionality when creating orders etc. We never require you to sign up when creating an order in the frontend.
For some odd reason there are around 20 orders that doesn't have customer data, either the firstname, lastname or email column are null. This data is null both in sales_flat_quote and sales_flat_order and sales_flat_order_address. The columns "created_at" and "updated_at" in the sales_flat_quote table are null as well. The funny thing here is that the order is created and processed but the customer doesn't receive a notification email since the email provided to the order model was never set (or for some reason deleted during the process).
Any clues what the issue could be? Have you ever experienced this problem?