I entered the following code in Maple 15.  In one instance it plotted the correct graph with the "x" and "y" labels exactly where I wanted them.  The identical code, in another instance (and again in a separate tab) generates an error:

  "Error, (in plots:-display) cannot make plot structure from object with name textplot"

Of course, when I click the error above in Maple (it is a link), a Maple webpage comes up that says: