If one banches one's codebase, e.g. in SVN, the UML diagrams in the branch will be blank. This is because the .grn file contains hard-coded references to the Eclipse project folder which do not get updated to the new branched project's location. Work-around: Use a text editor to edit the .grn file and globablly search and replace the old project folder name with the new one.
We're planning on making the .grn files encode project information only for elements which are not in the current project (we'll encode a full/absolute path for those elements). For any elements that are in the current project, we will encode a projectless/relative path in the .grn file, which defaults to the current project when the file is loaded. This will go out to the requestor ONLY at this point, as a field test. If this seems like a sensible approach to take, we will incorporate into a future release.
We have a solution for this. Fix will be incorporated into next release, which is targeted for end of April.