When mining, I'm often able to move my avatar away from the rock my pick is swinging at. Sometimes it's as little as 10 pixels, sometimes it's 600+ pixels.
I have screen shots if needed.
Here's how I recreate it:
1. Find a rock.
2. Click it.
3. Hover over the "mine" button
4. As you click "mine", also jump, or move right or left.
Sometimes you can get pretty far.
Once you've done this, you can't move until the mining operation is complete.
Environment Details:
OS X 10.6.2
Flash 10,1,53,64
Firefox 3.6.8