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/PartiallySynchronizedDocument.java
synchronized (getLockObject()) {
            super.replace(offset, length, text);
        }
	}
	
	/*
	 * @see IDocumentExtension4#replace(int, int, String, long)
	 */
	public void replace(int offset, int length, String text, long modificationStamp) throws BadLocationException {
		synchronized (getLockObject()) {
            super.replace(offset, length, text, modificationStamp);
        }
	}
	
	/*
	 * @see IDocument#set(String)
	 */
	public void set(String text) {
		synchronized (getLockObject()) {
            super.set(text);
        }
	}
	
	/*
	 * @see IDocumentExtension4#set(String, long)
	 */
	public void set(String text, long modificationStamp) {
		synchronized (getLockObject()) {
            super.set(text, modificationStamp);
        }