The tinymce.html.Node.isEmpty() is broken in that it will consider the following to be empty:

<pre>    </pre>

Even though it is meant to preserve white space for elements like PRE where white space is significant.

The fix is to change the signature of the method from isEmpty(nonEmptyElements) to isEmpty(schema).

The schema will provide the implementation of the isEmpty method access to:

• nonEmptyElements via schema.getNonEmptyElements()
• whiteSpaceElements (like PRE) via schema.getWhiteSpaceElements()

The implementation should be fixed to respect both these kinds of elements.