Hi,
Again, I don't see why it would do that. At least, not something in HikaShop.
But I don't know how you configured your website. For example, if you have a SEF extension like sh404SEF, it's probable that it comes from something there.
I can propose a few things to try to circumvent the problem:
- try deleting the category and recreating it. That might help.
- if not, try recreating it with another alias.
- if not, try recreating with an alias starting with the id of the category followed by a dash and then the alias of the category.