I have this issue with sql management studio 2014.
When creating a new database diagram and when I add existing table to a new diagram, the data inside a table is obsolete. I tried both dragging a table from list of tables and refreshing a table listing when using "Add table" function, but the result is the same. I have noticed this when I expand column list in object explorer, the actual columns are different then the columns of same table inside a diagram.
Did anyone experience the same problem, and how do I avoid this issue since it is very annoying and caused me a lot of unnecessary problems? If nothing else, I will have to try with a new version.