Paul Woddy & I picked up this when we were at AU2012, whilst helping out in a labs class, it seemed to elude us & maybe a few others as well. It relates to the naming protocol of Elevation Base parameter in Revit 2013. As far as we could both remember, up until Revit 2013 your Elevation Base constraint parameter was either Project or Shared. The image below is from Revit 2012.
The Revit 2012 help describes Elevation Base as follows.
If the elevation base value is set to Project, the elevation reported on a level is with respect to the project origin. If the base value is set to Shared, then the elevation reported is with respect to the shared origin. To change the shared origin, you can relocate the project.
Now lets see what appeared in Revit 2013! For some reason the Elevation Base Point parameter names have changed. I can see why this has happened, maybe for consistency with the away you approach shared coordinates & levels, Neither the less naming is confusing! Why point? When architects talk about a height, typically we talk about a level, not necessarily a point.
The Revit 2013 helps describes Elevation Base as follows:-
If the base value is set to Survey Point, then the elevation reported is with respect to the fixed survey point.
At the end of the day, its not a big deal, but these minor changes need to be watched for.