Bug 96917 [implementation] If two editors use the 2.x-compatible API, one or both doesn't work
At least one problem is that 3.0 installs partitioners for every editor that might possibly edit a file, but each editor expects its own partitioner to be installed. Leading to the famous white screen with blue line.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitDocumentProvider.java
});
			} finally {
				subMonitor1.done();
			}
			IDocument document= info.fTextFileBuffer.getDocument();
			IResource resource= info.fCopy.getResource();
			Assert.isTrue(resource instanceof IFile);
			/* https://bugs.eclipse.org/bugs/show_bug.cgi?id=98327
			 * Make sure file gets save in commit() if the underlying file has been deleted */
			if (!resource.isSynchronized(IResource.DEPTH_ZERO) && isDeleted(element))
				info.fTextFileBuffer.setDirty(true);
			if (!resource.exists()) {
				
				IProgressMonitor subMonitor2= getSubProgressMonitor(monitor, 50);
				try {
					createFileFromDocument(subMonitor2, (IFile) resource, document);
				} finally {
					subMonitor2.done();
				}
				return;
			}
			if (fSavePolicy != null)
				fSavePolicy.preSave(info.fCopy);
			IProgressMonitor subMonitor3= getSubProgressMonitor(monitor, 50);
			try {
				fIsAboutToSave= true;
				info.fCopy.commitWorkingCopy(overwrite, subMonitor3);
			} catch (CoreException x) {
				
				fireElementStateChangeFailed(element);