I did get a hold of someone in CS at the time. First I was told that no one else has reported this issue, and I directed them to this thread and another I had found online. Then they told me this is just how QB works and there is nothing I can do to override it. If I want to ensure that this issue does not happen, I should not have two people entering invoices at the same time, or let QB choose my invoice number. My response was I CANNOT let QB assign the invoice number as these are already pre-determined with a delivery ticket. Also, what is the point of paying for multi-user? (especially the high price through Right Networks) The whole point (in my situation) was to have someone help with the entering of stacks of invoices, which we must do at the same time.
Thank you for your help though.