When reading a webpage in Safari with the arrow keys (Quick Nav off), VoiceOver sometimes gets stuck in one area and keeps looping through a small subset of the elements on the page. Pressing vo-left or vo-right a time or three clears it up. I have not found a way to consistently reproduce this.
Bug First Encountered
How often the bug occurs
Simply press vo-left or vo-right to move focus, and things return to normal.