Multiple simultaneous index creation on distributed tables?

If you connect to the coordinator using multiple simultaneous connections and issue a series of CREATE INDEX statements on the same table, the indexes will run in series, where index B only starts being created on all workers once index A is finished on all workers.

The PostgreSQL 10 documentation makes it clear that it is possible to create multiple indexes on the same table in parallel:

https://www.postgresql.org/docs/current/static/sql-createindex.html

This issue is being opened to clarify expected behavior and/or request parallel index creation if this is not currently expected behavior.