It's the feature of the browser / server to give back stale "cached" information if the information is not expected to change within a period of time, saving the web server from unnecessary work. Happens most often with pictures and JavaScript files, etc. Information is usually cached based on the url, so if you edit the url to make a superfluous addition, the response will come directly from the web server. Generally speaking users should not need to be aware of this because it shouldn't happen - however something in how ImgFlip is configured or programmed is causing this issue.