I was attempting to get the JCK Editor to display a subset of styles from the custom style sheet in the editor's style drop-down list box. However, whenever I changed the "Use Custom CSS Classes for Styles ComboBox" to point to my file editor.css which was stored in the template's css directory, I would get a dropdown list where most of the entries were invisible (white on white I guess). A couple of them would show up just to make it even more confusing. If I pointed it to the template.css file of the template, the list would appear fine but of course it was much too long since it included all the styles from the template.
It turns out that the issue is caused by using the file named editor.css. I don't know if there is a caching issue or some setting buried deep within Joomla but when I created a new file named editor_template.css and stripped it down to just a few styles and everything worked just fine.
So inexplicably, the issue seemed to stem from putting the styles in a file named editor.css rather than another name such as template_editor.css. I have a solution but I don't really know why.
According to Tech Support, this is the proper solution:
It is probably this in your stylesheet that is causing the issue:
#mainmenu ul li a {color: #fff; text-decoration: none;}
I would add the below to your template CSS or the JCK Typography:
li.cke_panel_listItem a,
li.cke_panel_listItem a:hover,
li.cke_panel_listItem a:focus {color: #000;}