deleting order error

Hi guys,
I'm not sure if this is a bug but i have tried this many times when testing orders.

Basically what i do is make a purchase using either cash on delivery or paypal order (sandbox) the order goes through fine. However when i come to delete the order i go into Sales > Orders > select the order that i want to delete from system > press the delete button. Once i do this this error appears:
I'm not sure what this means but after i refresh the page the order disappears.

I hope someone can help sort this out

thanks
P

You might want to use the search first next time, or check the BUG topic that belongs to you version of OC.

Always mention version of your OpenCart!

- BUG: Deleting orders throws error "Notice: Undefined index: subtract" [FIX]