Back-Order Problem – Stock Quantity of 0 resets to 99999

We have problem with your plugin.
When Back-Order is setup for “Allow , but notify Customer” and when Stock Quantity for product is set to 0 problems happens when someone order this product because quantity becomes suddenly 99999 instead of staying on zero or instead of going negative.
Could you please tell me how this can be fixed because now our website doesn’t handle back orders, which is causing us loads of problems.