Thank you, that was helpful. We were capturing the DataChanged event from the spell checker, not the dictionary. We changed:
radRichTextBox.SpellChecker.DataChanged += RtbComments_DataChanged;
radRichTextBox.SpellChecker.GetCustomDictionary().DataChanged += RtbComments_DataChanged;
Now, the DataChanged event is firing when removing a word, or deleting all entries from the custom dictionary.
I have a follow-on question: Is there an easy way to tell what happened in the DataChanged event? It seems the EventArgs are always empty, and the only way I can tell to see what changed is to somehow inspect the Words collection in the sender object. It would be helpful to know if one word was changed, or the collection was emptied.
Thanks again for your help,