Hi,
You have to disable the chosen library (there is an option in HikaShop) for that.
I can't tell you why but your chosen shouldn't initialize these select. We put a class "chzn-done" to not have chosen on it.
But it looks like your chosen does not want it. You might have an extra script which remove the class or force chosen on all select.. I don't know and I am sure that it is not done by HikaShop.
The class "chzn-done" is placed by chosen when a select has been initialized. Placing this class on a select prevent the initialization of this lib on the specific select.
The class is in your HTML source code (when you see the source of the page, the inspection of the DOM is not the right way to see that) so for me, it should work fine and this chosen dropdown shouldn't be there.
So, there is something around HikaShop which break it.
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.