Hi,
Thanks for the report.
You're right, when you are trying to update an address using the new ajax system ; if the address save is forbidden (due to a VAT wrong number for example), the ajax return does not display the message because it's not a classical Joomla call.
We will see to improve that in the next release ; it requires some development and some tests.
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.