Hi,
In which section do you add your users (front-end / backend) ?
Can you reproduce the reproduce the issue in the HikaShop demo website ?
If so, can you please describe the process you're following ?
Please note that in the case when the user already link with another vendor, the vendor saving should not move the user from a vendor account to another.
In the front-end, the addition of a user requires the email of an existing Joomla user. Because it's not obvious we added an info icon with a tooltip and some explanations ; and like in the backend, if the user is already linked, it can't save it a second time.
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.