fcksavedurl within links

A simular question has been placed here a few weeks ago, but without response.
Following problem: Switching form the source view back to the preview mode FCK alters given a tags, changing the value of a given class attribute. The original value is overwritten by an _fcksavedurl.

This can be produced easily with the official demo under http://www.fckeditor.net/demo/ - just go into the source view, add a <a href="" class="pleasekeepthisasitis">foo</a> back to the preview and return to source view again.

Question: How to prevent FCK form changing the class attribute? (by the way - what sence is there replacing the atrribut value by classname for an unexisting class?)