I learned something about my Blendtec blender. During use, if it ever starts moving across the counter with a lot of torque, it probably has something stuck under one of the blades.
When I blend frozen things, it will often vibrate, and I have to hold the lid on to keep flying frozen fruit from knocking off the top. However, yesterday, the blender began doing something I hadn't experienced. It was moving across the counter with such force, I had difficulty keeping it in place. Near the end of the blend cycle, it started to smoke, and then it shut down with an "over-temp" error message.
It smoked a lot, filling my kitchen with a burnt smell all day. I was worried I had permanently damaged it, but later that day, it worked fine.
I believe a wedge of frozen peach or banana was lodged under one blade, which caused the strong sideways movement due to it being out of balance.
Moral of the story: If your blender starts really lurching to one side with a force greater than you've experienced in the past, power it off and check for things lodged under the blade.