Your poll is missing an option....the "nothing's wrong" option.
The refresh button changes to a stop button when something is being loaded in the current chrome tab. When you reload the page, something starts to load (e.g. like a facebook like button or google +1 button) after the page has rendered.
Because something is being loaded, the refresh button changes to a stop button (in case you want to stop the current action) but because it occurs so fast, it looks like the refresh button is "flickering"
Like I said, external API buttons (like twitter, facebook, or google) are usual culprits, but definitely not always - anything that is loaded into the page after the page has been rendered will cause this effect.
Hope that helps.
I've switched careers...
I'm NO LONGER a scientist,
but now a web developer...