Several XHTML properties may be updated when editing with the TinyMCE editor

Steps to reproduce

When editing an XHTML property using tinyMCE, other XHTML properties than the edited one may be updated with the changed content.

This is only reproducible on pages with many XHTML properties. 

The problem is that in TinyMCEEditor.js the global event tinymce.onAddEditor is used to perform initialization but no check is done to assure that the tinymce instance that triggered the event is the registered one. Consequently, when there are many tinymce instances and initialization takes a while, an editor may be initialized for the wrong property.