Context menu not displayed for some remote control keys

I have installed TV Headend and the frontend on Kodi (v17 RC3 via Libreelec on a RaspberryPi).
To control Kodi I am using the remote control that came with my TV (using CEC support from Kodi).

As I do not have a Menu/Options button that is unused by the main TV functions and could be used to open the context menu, I have used the keymap editor add on to assign one of the colored keys to open the context menu.

This is working for all parts of Kodi fine, but in the TV part I can only use it to open the context menu in the “Guide” section, but it does not work in the “Recordings” or the “Timer” section. This means I cannot delete a recorded tv program via the remote for example
I have already figured out that the context menu can be opened properly if I assign the rewind button (key code 226) to the context menu as a test, however this is not a permanent solution as this removes the original purpose of the rewind button in other parts of Kodi.
The color buttons are my only possibility to assign one of them to execute the context menu, but neither for the red button (key code 251) nor for the blue button (key code 254) the context menu is working in the two sections.

I believe this is a bug, is this then the right forum to post it?

Thanks for all the work on Kodi, this is a great piece of software