I got a PPS issue. Here is the steps I did:

1) I created/open a server pps for other services to use. And listen to it.
2) Client1 open it, send a message to my pps. Not close it. I got the message.
3) Client2 open it, send a message to my pps. Not close it. I got the message.
4) Client1 send a message to my pps again. I don't got this message this time, but I got a message saying Client2 close 
fd of my pps.
5) Client1 send last message again. Now I got previous message and this message.

Question:
Step4) This is wired that Client2 shouldn't have any knowledge of Client1. Why it can close its fd after Client1 sent a 
message? Is it possible that it open this pps with 'server' as well? Why can't I get the message from Client1? It goes 
to Client2?
Step5) Why I can get previous message now?

I am so confused, please give me some hints. Any idea/comment is welcome. Thank you.

Shuo