Thanks Pradeepa.
Looks like you have a version of TX Text Control there. The difficulty we faced with implementing with TX, was that there was no way to mark the reason why a word is flagged as an error. There are spelling error reasons like 'misspelling', 'incorrect case' and 'duplicate word'. The suggestions generated depend on the type of error.
So it looks like after the word has been added, for some reason "Thurston" was flagged again. Like you I cannot reproduce it. It might be reflagged because of something about the document. When an error is flagged, but is actually in the dictionary we have to assume that it's a 'duplication' error (hence the suggestion).
It's made more tricky by the integration with TX Text Control, since we rely on it to request text to be spell checked, and handle what RapidSpell says are errors. So we don't have much control.
The only workaround I can see is to set the RapidSpellDialog.WarnDuplicates property to false.
Jim
-your feedback is helpful to other users, thank you!