Invoice ID's are incrementing 2 at a time

According to my investigation this scenario happens when the following occurs:
Sample:
Current Order ID: 5

Client 1 added a product in the 'new' cart but he didn't checkout yet because he is sitll browsing in the store(New current order id: 6), Meanwhile Client 2 Added a product into his 'new' cart and he checkout first before the client 1 does(New current id: 7) So if the system admin check the order id, it will look like it is been incremented by 2 since the order id 6 is already been reserved by the Client 1. I "think" this is just a precautionary feature to avoid colliding orders when we will have hundred-thousand clients ordering simultaneously.

Another thing to note is that whenever a client confirm an order it creates another empty record with the same sessionticket_ticket and user_id and an invoice_id with a value of 0(see attached). This record will be filled the next time the same client order an id.