Found another 2 bugs. Had these two bugs before and spent a long time to find out how to reproduce it. Let me know if you need more info. You have my btc address 
Bug 1
To reproduce: When you have low in USD fund, buy BTC that is higher than your fund and switch the option to buy at market rate.
Bug: The system will let you proceed anyway and created an order id, however when you check the order, it is cancelled right away. You may check Order OV6OYZ-JSLCK-3DXH6O
Proposed solution: System should not waste the resource to create id if the user clearly does not have fund to complete the order. System can check the current market rate and do a calculation, compare it against user's fund and decide if a new order should be created.
Bug 1
To reproduce: When you have low in USD fund, buy BTC that is higher than your fund and switch the option to buy at market rate.
Bug: The system will let you proceed anyway and created an order id, however when you check the order, it is cancelled right away. You may check Order OV6OYZ-JSLCK-3DXH6O
Proposed solution: System should not waste the resource to create id if the user clearly does not have fund to complete the order. System can check the current market rate and do a calculation, compare it against user's fund and decide if a new order should be created.
Maybe I'm misunderstanding you here coinator, but if you create an order which you don't have the funds to complete, the system does let you proceed and will give you a partial fill for what you do have the funds for. The remaining partially completed order will be cancelled. If this is what you are talking about, it isn't a bug. If it isn't what you are talking about, please clarify.