Hi,
I can't reproduce your problem in your website.
I successfully upload an image for a category, save it, see that the image still there, remove it, save it, see that the image was removed.
But maybe you are in another context than mine.
Please provide more information. All useful information.
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.