BUG: DELETE USING SELECT IN SUBQUERY

Hello,
   When I try followed query, there is not deleted records (but shoul be 
deleted).

CREATE TABLE a (
  id SERIAL,
  name VARCHAR(50),
  CONSTRAINT a_pk PRIMARY KEY (id)
)

CREATE TABLE table_b (
  id SERIAL,
  fk_id INTEGER NOT NULL,
  name VARCHAR(50),
  CONSTRAINT b_pk PRIMARY KEY (id),
  CONSTRAINT b_fk FOREIGN KEY (fk_id)
  REFERENCES a (id) ON DELETE CASCADE
)

delete from TABLE_A where TABLE_A.ID in (
         select A.ID from TABLE_A as A left join TABLE_B as B on
                  A.ID = B.FK_ID
         where B.FK_ID is null)


  When I try it run separately (first select and then delete) it works fine.

  Is it a bug in SAP DB ?

  Thanks for answer,
  Julian