cache lookup failed for constraint when alter table referred bypartition table

Hi,

I am getting cache lookup failed for constraint error on master and 11beta3 with below test case.

[edb@localhost bin]$ ./psql postgres
psql (11beta3)
Type "help" for help.

postgres=# CREATE TABLE non_part (a INT,PRIMARY KEY(a));
CREATE TABLE
postgres=# CREATE TABLE part (a INT REFERENCES non_part(a)) PARTITION BY RANGE(a);
CREATE TABLE
postgres=# CREATE TABLE part_p1 PARTITION OF part FOR VALUES FROM (MINVALUE) TO (MAXVALUE);
CREATE TABLE
postgres=# ALTER TABLE non_part ALTER COLUMN a TYPE bigint;
ERROR:  cache lookup failed for constraint 16398