Kovid, sorry for the massive delay in my response (and after you responding so promptly!) I never received an email notification that there'd be a response in this thread.
That said, I'm very confident there's no other instances of calibre running in the LAN, there is however a DLNA server for the PS3 and I had just installed the latest calibre over the top of an existing version (I did shut calibre down, but perhaps it didn't shut down all it's processes...).
I'll make some time to examine this more closely over the weekend.
