Attribute promotion/demotion in Galera Cluster

Testing attribute promotion/demotion during a Galera RSU did not work. Led to node inconsistencies and even loss of the whole cluster.

MariaDB documentation is not clear about if this feature is supported or not.

In one source there is no comment about Galera:
https://mariadb.com/docs/server/ha-and-performance/standard-replication/replication-when-the-primary-and-replica-have-different-table-definitions

In an other source there is a vague indication that it should work in Galera:
https://mariadb.com/docs/server/ha-and-performance/standard-replication/replication-and-binary-log-system-variables#slave_type_conversions

It should be made more clear in documentation if this feature/behaviour is supported or not. And if it is supported, this IMHO is a clear bug in MariaDB Galera Cluster.

Blog article about it will follow...