Hello,
What I meant to say is(without going into stateful/stateless):
Let us say you have applied a filter on ge-0/0/0 interface for traffic sourced from A to anywhere as below:
A -------- ge-0/0/0.0 (EX) --------------------- External.
With this filter any reply to the traffic that was originated from External to A will also get affected.
Regards,
Rushi