Picture this. Open straight stretch of dry road, clear sunny day, 360 degree visibility for miles, not another vehicle within at least a mile in any direction. You decide to open her up. There's a 25 mph crosswind and as you hit 110 mph the bars start to shimmy. You say to yourself "Oh please, not a tankslapper." So you slowly back off the throttle and a few seconds later there's a bang down in front and you think, "Oh please, not a blow-out" then out of the corner of your eye you see a black thing flying out from the bike at knee level.
U turn, park, hunt it down in a field and examine the evidence to piece together what happened. It's melted through the Powerbronze logo and there's a bunch of melted plastic solidified above the top right edge. The right side of the tire is thoroughly scoured black.
Apparently it let go on the upwind side first, allowing it to drop against that side of the tire, scuffing the side of the tire and melting through the PB logo and part of the top edge of the extender from the inside. After a few rotations the tire torqued loose the other side and gave it a good throw.
It happened too fast and was over too quickly to be scary. Nothing bad happened to me or the bike, even the fender is undamaged. But I suppose it could have been worse.
Even the extender itself is still in good enough shape to re-use, but I think I'm going to leave it off for the time being.