BUG #15851: Concurrent Refresh of Materialized views not preserving the order of the underlying query

The following bug has been logged on the website:

Bug reference:      15851
Logged by:          Sai D
Email address:      sai.dulla@berkeley.edu
PostgreSQL version: 10.5
Operating system:   Ubuntu 16.04.10
Description:

Tests Run:
Materialized view refresh concurrently with unique index: 
Sort order is not the same as that of the output of the underlying query

Tested with Unique Index key that is the same as the sort order columns in
the underlying query. 
Results: Incorrect sort order after refresh concurrently
Tested with Unique Index key that is different from the sort order columns
in the underlying query. 
Results: Incorrect sort order after refresh concurrently


Materialized view refresh with unique index (Plain refresh, no concurrently
key word in the refresh command): 
Sort order is the same as that of the output of the underlying query