Zenith said the rating should be seen as a reinstatement of the old rating before the move.
"The fund was reinstated back to a recommended rating following a brief period under review whilst the team transitioned to Bentham," Zenith senior investment analyst James Tsinidis said.
"The fund has been a mainstay on Zenith's recommended list since it was first reviewed in 2004 and we have a high opinion of Richard Quin and his team."
Zenith reinstated the rating based on the investment team remaining stable after all team members crossed to Bentham, while the strong communication linkages between Bentham and the Credit Suisse Credit Investments Group stayed in place following the establishment of a formal sub-advisory agreement.
Zenith also indicated that it expected Bentham to benefit from the strong support of Challenger.