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
return fIsActive;
			}
			/*
			 * @see IProblemRequestorExtension#setProgressMonitor(IProgressMonitor)
			 */
			public void setProgressMonitor(IProgressMonitor monitor) {
				fProgressMonitor= monitor;
			}
			/*
			 * @see IProblemRequestorExtension#setIsActive(boolean)
			 */
			public void setIsActive(boolean isActive) {
				fIsActive= isActive;
			}
			/*
			 * @see IProblemRequestorExtension#setIsHandlingTemporaryProblems(boolean)
			 * @since 3.1
			 */
			public void setIsHandlingTemporaryProblems(boolean enable) {
				if (fIsHandlingTemporaryProblems != enable) {
					fIsHandlingTemporaryProblems= enable;
					if (fIsHandlingTemporaryProblems)
						startCollectingProblems();
					else
						stopCollectingProblems();
				}
			}
			private Object getAnnotations(Position position) {
				synchronized (getLockObject()) {
					return fReverseMap.get(position);