DROP OWNED BY ... CACADE & "could not open relation with OID" error

Hi,

I have been trying MADlib [1], a machine-learning library for PostgreSQL,
and when I was tying it on 9.5 and 9.6beta2, I often got following
error on my box.

------------------------------------
madpack.py : ERROR : SQL command failed:
SQL: DROP OWNED BY madlib_19_installcheck CASCADE;
ERROR:  could not open relation with OID 147056
------------------------------------

I wonder it could be a PostgreSQL bug or not.
AFAIK, this kind of error should not occur during regular SQL command execution,
so I guess this is a PostgreSQL bug.

Should I dig it down deeper to reproduce in a simple procedure?

Regards,

[1] http://madlib.incubator.apache.org/
-- 
Satoshi Nagayasu <snaga@uptime.jp>