It is possible to create (via import, but possibly in other ways) pages with editable areas which contain content which FCKEditor marks as dirty immediately upon loading. When this happens, if you view the page in edit mode, even if it isn't editable (due to workflow), navigating away from that page raises the "prompt to save changes on exit" message. This is a confusing message to get in cases when you haven't made any changes.

I believe making the following change in CMSScripts\cms.js solves the problem:

function FCKeditor_OnComplete(editorInstance)
{
    if (disabledFCKEditors[editorInstance.Name])
    {
		DisableFCKeditor(editorInstance);
		editorInstance.ResetIsDirty(); // add this line
    }
}

What that does is reset the dirty status after disabling the editor. With the status reset, the warning only appears if you really have made changes to the content, not when the editor has made those changes for you on first load.