Not sure if this helps figure this one out for you guys, but I'm seeing the same thing.
In my case, what I'm doing is this.
I have two PCs. One in my computer room. One in the living room that's hooked up to the surround sound. The PC in the computer room is the one with tons of drive space so it's the one storing my library.
All of my CDs are ripped to APE + CUE. I'm using APL files in the library.
My library is being served up through Library Server to my client PC. MC is finding its own port and picking 81. The client PC is configured to request files converted to MP3.
My client PC is running Remote Server on port 80. There are no conflicts.
If I sit at the server and connect to the client's Remote Server, I can change songs if I want. Inevitably, at some point when I click, IE will wait and wait and wait and eventually give me a page not found message. MC on the client has crashed.
I haven't done much extensive testing to see if this is due to clicking on things too quickly or just if it's something to do with my particular setup.