Hi Patrick,
I don't see this as a bug. You see, the whole idea of a multithread system is that you can reuse memory space without the need to create another thread. In my studies about the performance in AOLServer, I could see that the create/destroy proccess for a thread costs a lot of resources, especially I/O. So, it's a good idea if you can keep a thread alive to reuse later.
By the way, think about a large web site. If you are seeing a high memory peak, it's because the traffic is getting higher (thinking about it simply, of course), and it's not going to reduce instantly. So, it's much probably the memory space keeps alocated to nsd, until another request comes to use that area.
You see: I don't think it as a bug. It seems more like a strength in AOLServer to me.
