Yes, FileManager uses a smart trick for aggressive caching of thumbnails however this has a side effect when browser cache is disabled. Actually the trick is about authentication and caching together, i.e. first a request is made with state parameter so that the request is authenticated and browser caches the result, then a second request is made with a permanent cachable url and it's expected that browser loads the image directly from cache and not send a request to the server. This way for subsequent sessions, for example when you close the browser and reopen it, the thumbnails are loaded instantly (unless the source file is modified).
Developer Tools is not an issue because you opt-in to disable caching but yes some browsers can be confused when you press CTRL+F5 but if you press Enter in the address bar (revisit) the effect should be fixed automatically.
Maybe we can find a better way without side effects in future versions.