"Hide next move" in studies gets lost

[mliebelt]

Exact URL of where the bug happened

https://lichess.org/study/G8Q49yXj/qXhduLhP

Steps to reproduce the bug

1. Select chapter 1.
2. Go one by one through the moves of the game.
3. Check after each move the mode of the chapter (should be "Hide next move").
4. The moment you have played the last move, the former mode "Hide next move" is automatically switched to "Normal analysis".
5. Even if you play the moves back (to hide them again), and are then at the beginning of the moves list, the mode remains "Normal analysis".

What did you expect to happen?

The expectation of the study creator and user is:

• A chapter set to "Hide next move" remains in that mode all the time.
• Only when the study creator switches that mode to any other mode, only then the mode changes.

What happened instead?

The mode of the chapter switched to "Normal analysis", and the UI (when taking back moves) looked like the mode was "Hide next move". The next time you then go to that chapter, it behaves like "Normal analysis", so that all moves are visible then to everyone.

Operating system

Ubuntu 22.04

Browser and version (or alternate access method)

Chrome last (Version 133.0.6943.126 (Official Build) (64-bit)), or Chromium last (Version 133.0.6943.126 (Official Build) (64-bit))

Additional information

This is a bug that I have seen now at least 2-3 years, and today I took the time to hunt it. Reason is, that this one bug leads all the time to situations, where I show to the students (of an online training, where I share a study) the moves without intention, so that they see e.g. the solution, and the whole chapter does not work any more.