Hi,
We are currently working on a re-factoring of the "add to cart" system ; but it won't be available for the next release, it will be available later.
To prevent such think, the best is to put the button as "disabled" once you clicked on it.
The idea is to replace the javascript in the "add to cart" button to add a "this.disabled = true" when we authorize the "add to cart".
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.