Honda HRX mower wheels sticking when pulled backwards

I just purchased a Honda HRX-HXA a few months ago. It works great, even mulching on tough weeds. It keeps cutting where my previous HRC-215 would bog down.
However I ran into a small problem. When I pull it in reverse the wheels are supposed to spin freely. Lately the wheels have been sticking while in reverse. So it's real difficult to maneuver. It is intermittent. Sometimes if I make it drive forward, the wheels will un-stick next time I pull it backwards.
Is there something wrong with the transmission? I am hoping I don't have to take it in for warranty because I would probably have to leave it at the shop for a while.
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