Unable to remap “BACK” button from USB keyboard remote

I recently installed OpenElec 8.0 with Kodi 17. I have a USB keyboard remote from Lynec – https://www.amazon.com/gp/product/B00U78EKM4 – which has a “Back” button on one side. When I press this button, instead of going back, it seems to be opening the context menus instead?

I tried using the keymap editor to remap this button to the Navigation command for “back”, but it never seems to pick up this button that I’m pressing. Instead, it just closes the keymap editor and leaves the keymap setting the same as it was before. Can anyone help with this? Is it possible to remap this “back” button to ESC or BACKSPACE, which Kodi would then treat as normal?

Please help, thanks!