psql12.3 + jdbc_fdw - return wrong query results by using OR

Hello,

psql12.3 + jdbc_fdw(oracle18.x), tried:

[1]
select count(*)
from oracle_t1 as a
inner join local_t1 as b
on (a.c1 = b.c1);

return 100 records

[2]
select count(*)
from oracle_t1 as a
inner join local_t1 as b
on (a.c1 = b.c1
OR
a.c2 = b.c1
);

return only 2 records

(no null values in both tables.)

May I know what may cause the error please?

Thanks a lot.