There are some instances in Maya 2013 in which a user is modifying the UV of a particular mesh but viewport 2.0 is not updating as these changes occur. Image below shows viewport failing to register the changes made in the UV Texture Editor. While this is a known issue with our development team we have a simple workarond that can be used.
While one method is to simply switch back to the default viewport it may not show some of the more advance features such as a normal maps unless you go into the shading network and re-map the texture to show up in default viewport.
The other option is to simply make some changes to the UV's in Viewport 2.0 and force the refresh of viewport 2.0. in command line simply use the command below to reset the viewport.
This can be added to a hotkey or even a shelf button for quicker access.