I have engaged once or twice at full throttle, but I normally engage the PTO at 1/2 to 3/4 throttle which is what is specified in the manual. Hopefully, the new design of the belt will fix the problem. Any good mechanical engineer should be able to design a belt that would take even the stress of engagement at full throttle. I know there is a trade-off of cost versus design strength, but it's nice to know that some of you guys are getting some good reliability out of your belts.
I've got a Craftsman 26HP (backup) that's got over 260 hrs on it with the original belt, but my first single cylinder craftsman's first belt didn't last out the first season.
2009 Nissan Titan pullling a 18 ft PJ Trailer
2011 Kubota ZD326S (60") - 26HP Kubota Diesel
2008 JD Ztrak 830a (54") - 27HP Kawa
2010 Bob-Cat FastCat Pro 48" w/Accelerator (20HP Kawa)
John Deere JS36, 21" walk-behind
Blowers (Stihl BG85/Husqvarna 170BT)
Trimmers (Stihl KM110, FS90 & FS110, Kawa Multi-Tool)
Chainsaws (Stihl 260 Pro & MS460 Magnum)
& misc hand tools & equipment