The mainstream media should have no excuses for grammatical errors, with their experienced reporters and staff of editors, yet errors are not hard to find. Here's one from an article in this morning's Associated Press offerings:
"Fletcher is one of several lawyers who has represented Knight…"
The correct form, of course, is "have represented." The error is in thinking that "Fletcher" or "one" is the antecedent of "who", therefore "has represented." But the correct antecedent is "several lawyers," therefore "several lawyers who have represented."
However, add "the only" to the sentence and the antecedent becomes "one," making the singular verb correct:
"Fletcher is the only one of several lawyers who has represented Knight…."