Hi,
I review the code and make some tests, I can't reproduce your problem.
But the vendor categories can't be created like that without any event.
HikaMarket is triggering the event "vendor save" and "(joomla) user update" to check that the vendor category associated to the updated user/vendor exists ; and if not, it will create it.
There is also the creation automatic of the vendor when HikaMarket is loading the vendor (and the current user is not a vendor but have the right too).
Can you please check that you don't have duplicates vendors in the HikaMarket > Vendor section ?
Having an access to your website without knowing which event generate the duplication of category, won't help us to debug it.
So we have first to know how to reproduce the problem.
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.