Hello,
The fix will be include in the coming release.
Please note that the vendor selector type you're using is deprecated ; only the namebox type will be supported in the future.
Only the namebox allow to have a good interface when having a lot of vendors ; the dropdown mode was switching to a popup which is not good enough.
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.