Bug 137073 [Preferences] Encoding field editor never fires value change events
The class AbstractEncodingFieldEditor never fires VALUE property change events unless the validaty of the value has also changed. I will attach a patch that corrects the problem.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/ide/dialogs/AbstractEncodingFieldEditor.java
topControl = top;
		}
		GridData data = new GridData(GridData.FILL_HORIZONTAL);
		topControl.setLayoutData(data);		
		topControl.setLayout(layout);
		SelectionAdapter buttonListener = new SelectionAdapter() {
			public void widgetSelected(SelectionEvent e) {
				updateEncodingState(defaultEncodingButton.getSelection());
				updateValidState();
			}
		};
		defaultEncodingButton = new Button(topControl, SWT.RADIO);
		defaultEnc = findDefaultEncoding();
		defaultEncodingButton.setText(defaultButtonText());
		data = new GridData();
		data.horizontalSpan = 2;
		defaultEncodingButton.setLayoutData(data);
		defaultEncodingButton.addSelectionListener(buttonListener);
		otherEncodingButton = new Button(topControl, SWT.RADIO);
		otherEncodingButton
				.setText(IDEWorkbenchMessages.WorkbenchPreference_otherEncoding);
		otherEncodingButton.addSelectionListener(buttonListener);
		encodingCombo = new Combo(topControl, SWT.NONE);
		data = new GridData();
		encodingCombo.setLayoutData(data);
		encodingCombo.addSelectionListener(new SelectionAdapter() {
			/*
			 * (non-Javadoc)
			 * 
			 * @see org.eclipse.swt.events.SelectionListener#widgetSelected(org.eclipse.swt.events.SelectionEvent)