It is very possible that the ' symbol you enter is different from the one in the dictionary. For example the apostrophes in MS Word are somewhat special and if you copy "don`t" from Word, it will be underlined as a mistake. One of the suggestions should be "don't" with a slightly different apostrophe.
If that's not the case in your application, we would appreciate it if you could open a support ticket and send us a sample project so we can investigate the issue further.
the Telerik team
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