create or alter procedure p_ins(a_id int) as begin end;
recreate table t(id int not null primary key);
commit;
create or alter procedure p_ins(a_id int) as
begin
  insert into t values( :a_id );
end;

commit;
set term ^;
execute block as
begin
  rdb$set_context('USER_SESSION', 'SEEN_FROM_WHEN_CASE_1', null );
  delete from t;
  begin
    insert into t(id) values(1);
    insert into t(id) values(2);
    insert into t(id) values(3);
    insert into t(id) values(3);
  when any do
    rdb$set_context('USER_SESSION', 'SEEN_FROM_WHEN_CASE _1 ', (select list(id) from t) );
  end
  
  rdb$set_context('USER_SESSION', 'SEEN_FROM_WHEN_CASE_2', null );
  delete from t;
  begin
    insert into t(id) values(1);
    insert into t(id) values(2);
    insert into t(id) values(3);
    execute procedure p_ins(3);
  when any do
    rdb$set_context('USER_SESSION', 'SEEN_FROM_WHEN_CASE _2 ', (select list(id) from t) );
  end

end
^ set term ;^
rollback;

set width seen_in_when_1 10;
set width seen_in_when_2 10;
set list on;
select 
   rdb$get_context('USER_SESSION', 'SEEN_FROM_WHEN_CASE_1' ) as seen_in_when_1
  ,rdb$get_context('USER_SESSION', 'SEEN_FROM_WHEN_CASE_2' ) as seen_in_when_2
from rdb$database;
set list off;
rollback;

SEEN_IN_WHEN _1                   1,2,3
SEEN_IN_WHEN _2                   <null>