Cannot enter a name with an apostrophe

Cannot enter a name with an apostrophe (or single quote) when registerring, e.g. John O'Brian. Surprised to see nothing in forums about this except a suggestion to edit 'Field entry validation' which we tried every option and still nothing works, we get an error alert: "Please enter a valid Username. No spaces, at least 2 characters and must contain only letters and numbers."

We are hiding the username at registration as we are only using the email address (to make it easier for our members) and can see that CB creates the username from the firstname and lastname fields separated by a space... so how do we either (1) set the username to accept anything, or (2) change how the username is created so we could have it remove special characters?

Any ideas would be helpful.