Incomplete Orders strangeness - Need help!

[OCSpeaker]

I've had many customers recently tell me they are unable to complete their order. Out of curiosity I looked in the "Not Completed" tab of the orders section in Admin. I noticed that the customers who were unable to complete their order were in "single checkout". We DO NOT have "Single Page Checkout" enabled. So how could this be happening? Does anyone know of a fix? I have attached a screenshot.

Thanks,
Eric