Played this game like 15 years ago, wild it's showing up here somewhat translated now, but I remember clear as day struggling with the exact thing you're talking about here.
It's not bugged, it's a "trap" to throw you off where they start swapping the buttons around after each screen. Which makes it... Pretty damn difficult for someone who isn't fluent in Japanese to beat. You have to memorize each of the buttons, which are:
- 左側を進む - Left
- 中央を進む - Center
- 右側を進む - Right
- ジャンプ - Jump
- 水の中へ - Fall in the water. (There are two of these on the bottom left / right. They are trap options, which come mainly into play when they start swapping buttons around.)
I recommend simply memorizing the first letter of each option rather than the entire word, this should help you to parse the information quick enough. Hopefully this information helps someone out.