Comment 3 for bug 1523506

I believe everything works as expected. Where I think your reasoning is wrong is what you think makes a host belong to the default AZ.

As I see things "bar" does not belong to an AZ at all, only aggregates that explicitly define the AZ attribute "belongs" to an AZ (strictly speaking, only hosts in that aggregate belong to the AZ, but anyway).

What makes a host belong to the default AZ? Simply that none of the aggregates it has been added to has the AZ attribute set. So, from your steps above, up until 3) node2 belongs to the default AZ and after 3) it only belongs to the AZ named "az", which also is what the "nova availability-zone-list" command shows.