How can send diameter commands in two sessions?

Question

I am designing a seagull scenario look like:

Client --------------- Server
--- CER -->
<-- CEA --- --- AAR --> // the first session
<-- AAA --- --- AAR -->
<-- AAA -- <-- RAR -- --- RAA -->
--- STR -->
<-- STA -- --- AAR --> // the second session
<-- AAA -- <-- RAR -- --- RAA -->
--- STR -->
<-- STA --

But in the second call, we saw an message in log "Expected AAR when receiving RAA.." . If we make the second call scenario same as the first call, (two AAR\AAA and one RAR/RAA) it was passed.

So that the question is "Is there any ways to control seagull flow as the scenario that we expected? "