Hello,
The HikaShop customer receives an email because the order status of his order changed.
I don't know why you are using a custom order status to mark which orders are paid but that is not something needed in HikaMarket which already store that information (when you use the vendor payment system).
The issue you have for the moment is strictly regarding HikaShop feature and by using HikaMarket workflow you should not have it.
Unfortunately, that's all I can tell you right now with the elements I got.
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.