The same physical control can have a different software identity
Kodi’s keymap manual distinguishes keyboard, remote, gamepad and other input sections. It notes that some remote adapters are presented as keyboards. A binding placed under the remote section will therefore not necessarily describe the event Kodi receives from that device. Record the actual input type and the screen where the intended action fails before changing several controls together.
A window-specific binding can override the global fallback
The manual explains that Kodi falls back to the global map when the current window has not bound the key. For an illustrative configuration, a key can have a navigation action globally but a playback-related action in a video window. That difference can be intentional. Check the applicable window name and action against the official reference rather than assuming that a successful home-screen press proves every window uses the same mapping.
Review custom files in their documented order
Kodi processes mapping XML files in alphabetical order, with later definitions adding to or overriding earlier ones. User mappings belong in the userdata keymaps directory; installation defaults should not be edited directly. Keep a copy of the small custom file being tested and inspect other overrides before declaring a new binding ineffective. Recheck both the affected playback window and normal navigation afterwards. A scoped mapping change should solve the intended control problem without silently changing unrelated screens.
Questions, answered
Is a global binding always the final action for that key?
No. A window-specific binding and later overriding keymap files can change the applicable action.