This happens on a slow connection, or when the game servers are too busy (have not tested my net traffic during this).
If I interact with a butterfly and the thing flies off my screen before html has finished downloading for the interaction menu pop-up, then the pop-up flies off the screen along with the butterfly. Typically the html would load before the butterfly has a chance to fly off the edge of the screen, but when the game lags it happens, and in Chromium on Ubuntu it renders outside the game world window.