Hi Hugo,
I have finally found the problem : the custom field category limitation.
With two variants and a category limitation for the custom field, it is not process correctly by the getInput.
Nicolas fixed the problem and I have update your store with the fixed version.
During my tests, I removed a variant for your two variants product. I have recreate it but I didn't have your colored images. Sorry !
But the good point is that the bug is fixed
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.