The display of ALTER DEFAULT PRIVILEGES statements can be incorrect.
I reported this bug in 2013, but it seems like it never got through:
http://www.postgresql.org/message-id/528C2D00.6010905@falter.at
Details, with steps to reproduce:
https://redmine.postgresql.org/issues/694
Just tested with version 1.20 again and the situation seems unchanged.
Regards
Erwin