[muscle] Question about server behaviour

I'm playing with MUSCLE 4.11 on my XP portable.
I've adjusted the server build to be a DumbReflectServer for convenience, and I have a couple of Java client apps - one of which pumps empty messages at the server, and one of which sucks in messages and counts the rate per second.
I also have a simple homebrew Java server implementation that implements Dumb by way of a learning tool for Apache MINA 2.0.
The behaviour of the two servers is different in a way that I had not expected. 

The Java server pretty much pumps messages as it receives them.
The C++ server, however, seems to prefer to read messages rather than to write them. If the sender application sends with little respite (a flush and 10ms sleep every 1000 messages) then the C++ server effectively just sucks in all the messages until the sender stops, and then they get spooled to the receiver.
If I increase the sleep time to 100ms then the message flow is even (at about 6000 messages per second with one sender and one receiver), with a little CPU spare on my machine. 

Is this expected behaviour?

James

Other related posts: