It's indeed caused by the browser. It simply takes the version that is cached without checking if it has been replaced. I'm aware of this behavior. I already added the timestamp at the edit page a while ago so you always saw the new versions there.
I now added the timestamp of the last edit to the image path everywhere to trick the browser caching system. So this problem hopefully shouldn't occur anymore.
btw: Closing the browser shouldn't be necessary. Using the reload/refresh function should have the same effect.