This is mostly an issue for slow/unstable internet connections, but this has been occasionally bothering me for a while now. The issue is only regarding the web app.
Expected behavior: Audio (regarding pronunciation of a word) only plays when the corresponding word is still being reviewed on the screen.
Actual behavior: If the internet connection is slow/unstable loading of audio for a word may be delayed. The audio is then played once it has been loaded, regardless of how many cards ago it actually was supposed to play.
Also a secondary minor issue:
When clicking twice onto the audio button in quick succession, the audio overlaps and plays at the same time. It would be better if any clicks on the same audio symbol, while audio is already being played, would be discarded.