RiverSource Investments, American Century Investments and OppenheimerFunds have received "F" grades from a Morningstar analyst for failing to explain recent changes to shareholders and adding to the paranoia of already shaken investors.

"It's about stewardship of a fund, but it's also about communication to shareholders," Andrew Gogerty, analyst at investment researcher Morningstar Inc., told Dow Jones. "None of [the moves] were explained."

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