Hi,
If you did your changes via the menu Display>Views or by editing the CSS file via the HikaShop configuration like we usually recommend, you should not loose your changes when you update/install again HikaShop.
I'm not sure what was the fix anymore for that bug. You can try editing the file "form_restrictions" via the menu Display>Views for your backend template and change the line:
explode(',',@$this->element->discount_category_id),
to:
explode(',', trim(@$this->element->discount_category_id, ',')),