Ah, it's actually advancing. Take a look at the dots "."
If you're pressing enter, the dots will increase. When it's 3 dots it will advance to next textbox. Or easier to check, if there's a mic image at the end of the sentence, that means pressing enter will advance to next textbox. If there isn't a mic image at the end of sentence, it means that sentence is not finished yet and pressing enter will show the next text (in this case, only a dot appears so it appears to not be advancing...)
But anyway, it seems to be causing misunderstanding, so I'll probably just remove those 3 dots thingy lol.