As of r38891 in the gsoc branch, any change to a HtmlEditor field will cause a confirm dialogue to show whenever new selection is made in the left tree even if the "Save" button has been clicked.
This bug was caused by r38620 which merged in TinyMCE 2.1.1.1 because after doing the following, the bug disappears:
svn up cms --revision 38619 && svn up jsparty/ --revision 38619 && svn up sapphire/ --revision 38619
My dev enviroment is as follows:
Apache/2.2.3 (Ubuntu) PHP/5.2.1
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.4) Gecko/20061201 Firefox/2.0.0.4 (Ubuntu-feisty)
Here is a hack that works around this problem: Hack-To-Fix-TinyMCE-Change-Detection-cms-gsoc-r38861.diff
Here is a gsoc trac ticket I filed about this Save reminder still shows after a page or newsletter draft is saved and a new selection is made in the left tree
I tried for quite a while, but was unable to fix this bug properly. Hopefully the above hack will help whoever works on this. ;)