Hi,
The "clean cart when order is : confirmed" will work correctly if the customer confirm himself the order.
That can be done with some specific payment plugin but for some other plugin, that setting can't work properly and the customer cart can't be clean.
If you confirm an order in the backend ; you have now way to know which customer cart you need to clean.
You can't know if the current cart is the right one ; maybe the customer has created a new cart... etc
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.