Removed from webmaster-group after login

-- HikaShop version -- : 2.6.3
-- Joomla version -- : 3.6.2
-- PHP version -- : 5.3.28
-- Browser(s) name and version -- : Safari 9.1.1

When I check out and are asked to log in, I enter my credentials. Actually I am within the group "webmaster". After logging in (during the checkout process) I'm removed from this group?! So I'm only in two other groups left but I don't have access to the backend anymore. That's weird!
I tested this a couple of times and this happened everytime.

Hi,

HikaShop starter can't do that.
You should take a look at the plugins installed in your website because the login is done by the Joomla core, even if you're in HikaShop that's related to Joomla itself.

Regards,