Resolution

If you already set some domain to be default for the specific IP address, this action can't be reverted and your cannot unset it in Plesk panel interface, you can only switch to other domain be default.

The solution is to manually set default_domain_id to zero for specific IP address directly in Plesk database, for example:

# mysql -uadmin -p`cat /etc/psa/.psa.shadow` -Dpsa -e "UPDATE IP_Addresses SET default_domain_id = 0 WHERE ip_address = 'IP.ADD.RE.SS';"

The following command will remove default domain setting for all IP addresses:

# mysql -uadmin -p`cat /etc/psa/.psa.shadow` -Dpsa -e "UPDATE IP_Addresses SET default_domain_id = 0;"

Then you need to run `websrvmng` utility to apply changes:

# /usr/local/psa/admin/sbin/websrvmng -a -v