I pressed submitt to answer a question.
At the same time someone else had also answered the question. The bar at the top of the screen showing that a new answer was available did not appear before I pressed submitt.
The result was that I got the bar showing a new answer was available, my answer did not appear as if it had been submitted. No buttons / links ... on the screen were active. I had to close the browser and reopen stackoverflow. My answer had been updated.
I use IE 7.