broken governor?

I was mowing with my HRB215 and out of the blue it revs up higher than I've ever heard it reving before. I released the safety bar to shut it down and I can't figure out what's going on. If I manually hold the governor arm back I can keep it under 3500, but That's what the governor should be doing on it's own right? The linkage is all connected and free, and I've re-adjusted the governor per the manual, but that's where it was adjusted already. The carb is clean as a whistle. Can the governor "break" inside of the crankcase? I don't look forward to taking that apart, but the grass is two inches taller every day. We've had sheep and goats in the "pasture" for 15 years, until a couple of months ago, but they're gone now and it's amazing how much they were eating because now I've got an additional couple of acres to get at, and it's getting daunting. I don't see any chatter about HRB215 governors online other than an english woman with the sdame symptoms a couple of years ago, and she got no helpful advice (that I haven;t double-checked already). Thanks for the benefit of any previous experience or ideas.....!

Did you notice any resistance to the governor arm when you moved it to drop the RPM ? If not, then I would say something has let go in the engine with the governor. You should have some resistance to moving the governor arm on any engine. The throttle spring tension pulls the engine INTO fuel and the governor force pulls the engine OUT of fuel. The balance between those two opposing forces is what determines RPM.