[roscore] Following the tutorials ... unexpected output?

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Hi guys,

Following the Tutorial #6.- "Understanding Topics Basics", at the first step (1.1.1.- roscore), quoting:

Let's start by making sure that we have roscore running, in a new terminal:

$ roscore

If you left roscore running from the last tutorial, you may get the error message:

roscore cannot run as another roscore/master is already running. 
Please kill other roscore/master processes before relaunching

However, if I let one "roscore" process running, and launch a new one in a different terminal Window, I get the following error:

ERROR: Unable to start XML-RPC server, port 11311 is already in use
Unhandled exception in thread started by <bound method XmlRpcNode.run of <rosgraph.xmlrpc.XmlRpcNode object at 0x8cd3e2c>>

And after the stacktrace:

socket.error: [Errno 98] Address already in use
ERROR: could not contact master [http://pfc-VirtualBox:11311/]
[master] killing on exit

So, my question is: Is this a kind of "bug" in the tutorial or may I worry about that error being threw instead of the suggested output @ tutorial?

Thanks in advance for your answer!