Cannot save product category image

-- url of the page with the problem -- : shop.movi.be
-- HikaShop version -- : 3.2.0
-- Joomla version -- : 3.7.5
-- PHP version -- : 7.0.21
-- Browser(s) name and version -- : Firefox 55 & Chrome 60

To put it simple, one of the categories created "Koopjes / Tweedehands" the subcategorie "computers" refuses to accept the image attached as categorie image. One can click edit categorie, on the right "image" click brows, browse to image, "computers.png" gets selected but when one presses any of the save options, the images doesn't get applied.

SU access can be given if needed

Fix confirmed. Thanks.