ERROR "This operation is not defined for system tables" WHEN CREATING A PRIMARY KEY ON FIREBIRD 3

I can understand that some new functionalities might not work on a beta/alpha release, but this is related to a primery key creation, so I can't see a plausable reason for it not to work.

Im trying to run a simple script, creating a table with a primary key.

CREATE TABLE hl_oids 
  ( 
     oid INT NOT NULL, 
     CONSTRAINT pk_oids PRIMARY KEY(oid) 
  ); 

and I get this

Cannot commit transaction:
This operation is not defined for system tables.
unsuccessful metadata update.
cannot create index PK_OIDS.

I created a discussion on Yahoo Firebird Group, but apparently it was delete, because you can ask anything in the Firebird Group, EXCEPT ask about problemas in ALPHA/BETA releases. What is that all about?

No wonder Firebird is almost invisible in the database arena these days..