When adding custom classes to the RadEditor for a DNN 7.2.0 install, the following instructions work without issue.

https://www.youtube.com/watch?v=ConUx96Swso

The problem arises when you make any edits to the Toolbar Configuration file.  For example, if you replace <tool name="PasteStrip" /> with <tool name="PastePlainText" />, the next time you edit content in the site, the CSS Class drop down will appear empty in the RadEditor.

Can anyone shed insight into this issue?