LEFT JOIN does not join on Oracle varchars about oracle_fdw HOT 6 CLOSED

EXPLAIN (ANALYZE, VERBOSE) SELECT COUNT(*) FROM table_a LEFT JOIN table_b ON table_a.char_key = table_b.char_key WHERE table_b.data IS NOT NULL;

 Aggregate  (cost=20192.16..20192.17 rows=1 width=0) (actual time=5462.986..5462.986 rows=1 loops=1)
   Output: count(*)
   ->  Merge Join  (cost=20099.66..20179.66 rows=5000 width=0) (actual time=5462.971..5462.971 rows=0 loops=1)
         Merge Cond: ((table_a.char_key)::text = (table_b.char_key)::text)
         ->  Sort  (cost=10049.83..10052.33 rows=1000 width=54) (actual time=2303.251..2357.638 rows=140903 loops=1)
               Output: table_a.char_key
               Sort Key: table_a.char_key
               Sort Method: external merge  Disk: 2880kB
               ->  Foreign Scan on public.table_a  (cost=10000.00..10000.00 rows=1000 width=54) (actual time=16.870..870.473 rows=140903 loops=1)
                     Output: table_a.char_key
                     Oracle query: SELECT /*4cf9caa95b92d7f20e5e94f87b23e6fa*/ "CBTA_PROPERTY_ID" FROM "SYSADM"."TABLE_A"
                     Oracle plan: SELECT STATEMENT
                     Oracle plan:   INDEX STORAGE FAST FULL SCAN TABLE_A
         ->  Sort  (cost=10049.83..10052.33 rows=1000 width=54) (actual time=2993.286..3018.576 rows=201788 loops=1)
               Output: table_b.char_key
               Sort Key: table_b.char_key
               Sort Method: external sort  Disk: 3800kB
               ->  Foreign Scan on public.table_b  (cost=10000.00..10000.00 rows=1000 width=54) (actual time=51.710..1466.675 rows=201788 loops=1)
                     Output: table_b.char_key
                     Oracle query: SELECT /*6a78ab8d19af030693e6008583982e1d*/ "EXECTIME", "DATA" FROM "SYSADM"."TABLE_B" WHERE ("DATA" IS NOT NULL)
                     Oracle plan: SELECT STATEMENT
                     Oracle plan:   TABLE ACCESS STORAGE FULL TABLE_B
 Planning time: 78.171 ms
 Execution time: 5464.724 ms

CREATE FOREIGN TABLE table_a (

    CHAR_KEY    character varying(18)   NOT NULL,
    COL_B   character varying(15)   NOT NULL,
    COL_C character varying(100)    NOT NULL,
    -- ...

) SERVER xxxx OPTIONS (schema 'xxxx', table 'TABLE_A');

CHAR_KEY    VARCHAR2 (18 Byte)  N
COL_B   VARCHAR2 (15 Byte)  N
COL_C   VARCHAR2 (100 Byte) N

CREATE FOREIGN TABLE table_b (

    CHAR_KEY    character varying(18)   NOT NULL,
    DATA    float8  NOT NULL,
    -- ...

) SERVER xxxx OPTIONS (schema 'xxxx', table 'TABLE_B');

DATA    NUMBER (9,6)    N
CHAR_KEY    VARCHAR2 (18 Byte)  N