I made this report in my initial review of the new interface, but the bug still exists so I’m now submitting it as a bug report. Also, I’m upgrading my assessment from “an annoyance” to being “highly irritating”.
Mark as Known change
…
When marking an item as known (using Alt+K), the interface now immediately moves to the next sentence.
…
I also noticed that if I hit Alt+K and then immediately hit the enter key (which is my current behaviour for most “mark as known” sentences), the new interface will frequently skip over the next sentence in the list, so that instead of playing 20 sentences in a batch, I might find that I only played 16. The other sentences would still be due to play/review as they didn’t get played, but this is still an annoyance, and it is also clearly a bug.