[bigpen23]

The thing is, is there anything to fix?

I decided to take a look at this.
Installed visual studio and everything to compile Kodi on windows again...

Started a debug session and started 3:10 to yuma as my uhd bluray test disc.

I can control the main menu.
I can start the movie from main menu.
I can toggle the pop up menu during movie with ctrl+shift+m, while this is happening it's possible to change subtitle/audio/chapter, pressing ctrl+shift+m again it goes away and I can skip chapters once more.

So, if I can't replicate the problem, there's nothing to look at.

Thanks for the response. When you change chapter/subtitle, did you use the popup menu to select items (instead of using keyboard shortcut) ? If yes, is it a Java disc ? (has files in ..\BDMV\BDJO?). Seems only java menu has this problem. For movies, skip chapters or change subtitle using keyboard shortcut is perfect fine. But for concert disc, select songs from popup menu is very important and many classical concert discs are Java unfortunately. Thanks again!

There are a few concepts that you need to understand to understand what I'm saying:

1. m_menu = true means, Kodi is inside a menu, so it's not playing a video, so it's expecting that the arrow keys you press move the cursor in the menu.
2. m_menu = false means, Kodi is NOT inside a menu, so it's playing a video, so the keys you press control the playback (fast forward, skip, chapters etc)

So when playing a disc you have 2 scenarios: 1 you are browsing a menu 2 you are watching the content.

So far so good, right?

Ok, the problem it's not JAVA, it is that besides a regular menu, you have pop up menus.

Now think like a bluray player:
If you are inside a menu, do menus have chapters? Do menus have fast forward? Menus are static, right?
Because of that while inside a menu, you can't skip a chapter, you can't fast forward, or else you would break the menu, correct?

Ok.. now imagine that for Kodi when you are playing a movie, that DO HAVE a pop up, while playing the movie, it still thinks you are inside a menu.
This causes problems, right? No fast forward, no chapter skipping. 

What is the problem, there's no way (at least that I know of) that is possible to tell if the pop up menu is on screen or not.
If there was a flag that we could use, we could give the user control over the popup menu during playback and when the playback menu is closed it would go back to kodi.

So what option remains? Give the user the freedom to select what he/she wants to control. 
When you press the popup menu key the m_menu state will change. If you press once and it's true it will be false and vice-versa. 

How can I tell the state of m_menu and what am I controlling?
Look at the current chapter, if you see left upper corner 00 means m_menu = true, means kodi think it's inside the menu, even if the movie is playing and the arrow keys you press will be sent to the blu-ray menu and not kodi.

If it says 01/22 or something means you are controlling Kodi.

If you want a way to break this you can do:
Start the main movie of the disc, press the pop up menu key (so m_menu will be set to true - because at every new content you play it is reset to false) now the popup menu is showing, correct?
Now wait for it to disappear or press on a close icon. 
What happened here? You haven't pressed ctrl+shift+m again, have you? so m_menu is still true, means kodi still thinks you are inside a menu, so everything you press will be passed to the disc, if you press up and the disc is programmed to open the popup menu with up, it will open the pop up menu.

if you press left or right and kodi move the playback in the timeline and you think this is wrong, that you would prefer to work with the menus, just press ctrl+shift+m again.

Before the commit I made, you could ONLY control the disc menus this causes:
Chapters not working.
Moving back and forward during playback to be broken

I could restore chapters during menus but that's not a good solution because if you press a chapter skip during playback it will break the playback.

Thank you again for your detail explanation. I think there are some misunderstandings. For those java discs I tested, the java popup won't disappear if I don't toggle ctrl+shift+M, so the m_menu status might actually be in sync. Let me explain again the problem and see if it can be replicated :

1. Open a BD Java iso file(with files in folder \BDMV\BDJO) in v19 (latest window built on 17 Jan 21)
2. Wait for top menu (same item as popup menu) to show up. Then select a chapter from the menu item.
3. Video content played correctly and menu is gone (so far so good...)
4. Then, when you want to "jump" to other chapter. You press ctrl-shift-m, and the popup menu appears.
5. But if you try to press the arrow buttons, it skips chapter/fast forward instead of controlling menu items. Popup menu won't disappear until you press ctrl-shift-m again...