SQL & PL/SQL :: Executing Select On Table Using DBLink From Oracle 9 To 11

I have something strange :

I am executing a select on a single table using a dblink from oracle9 to oracle11 and i don't know why automatically add in the select the rowid at the end. The problem is that inside the query i have a group by so it crash.

Query sample :

original query from vb:
select a, b, c
from mytable
group by a, b, c

query intercepted on oracle11:
select a, b, c, rowid
from mytable
group by a, b, c