I've noticed that thumbnail caching acts kinda weird especially when you use the 'Quit' button (or kill the app by system settings). Currently it only caches one video here (the one on the bottom on the attached video). The behavior is dynamic though. Sometimes it caches, sometimes it does not. You probably won't notice it if you leave the player by 'back' or 'home' button. This seems completely independent from existent network/cifs folders. Can you confirm this behavior?