Hi,
I guess that the upload works fine but when you save the product just after, the image is deleted.
The popup add the image to the product so you do not require to save the product just after.
The popup would add some HTML content into the form too. This HTML content contains the image identifier in order to tell that the image is linked to this product.
If the image is not used by any other product, HikaShop would try to remove it.
It means that, the html added by the popup do not work right for you.
I made some tests in my local website and I cannot reproduce it. Which Internet browser do you use ?
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.