Multiple resources, same user, who gets the message?

If a user is logged in from multiple resources both having the same priority:

me@domain.com/res1 and me@domain.com/res2

and a message is send to me@domain.com who will get the message??

for my purposes I would like for both clients to recieve the message, but currently only the client who last logged in will get the message

is this just a config issue?