Summary:

Keystroke emulation of programmable buttons on both Elecom HUGE trackball pointing device and Elecom DEFT trackball pointing device is not working as expected: Keystroke emulation fails for most in-game actions, such as changing the active inventory slot, but works in the in-game text chat interface.

Details:

Elecom HUGE trackball and DEFT trackball programmable buttons can be set to emulate keyboard keys, and this allows the buttons to be used to send keyboard keystrokes in Minecraft. For example, assigning a button to keyboard key "9" will allow a button press to switch the active inventory slot to slot 9.

This emulation was working in Java MC 1.12.2, but it stopped working in the next released snapshot (17w43a) and has not worked since. Emulated keystrokes are still being sent to the text / chat bar (i.e., when the chat bar is open, pressing the button assigned to keyboard key "9" will produce "9" in the chat bar as though the key had been pressed), but they do not work outside of the text chat interface. Emulation still works as expected in Minecraft for Windows 10 (Bedrock).

Bug still appears in (Java) both release 1.15.2 and snapshot 20w14a. Also confirmed for 1.13-pre1, 1.13.1, 1.14.1, 1.14.2, 1.14.4, and 1.15.  Launching Minecraft into 1.12.2 results in emulation working as expected.

May relate to, but does not appear to duplicate, MC-130857 and MC-131010.

Additional information:

Emulation of keyboard keys using Logitech Cordless Optical Trackman pointing device programmable buttons for Java MC works as expected.  (Tested using Logitech SetPoint Control Center current version: 6.69.126.)  Elecom emulation also works as expected in Minecraft for Windows 10 (Bedrock).

Elecom emulation / pointing device driver software in use: ELECOM Mouse Assistant (for Windows) Ver. 5.1.13.000 (= latest, dated 2019.11.06). Available: https://www.elecom.co.jp/global/download-list/utility/mouse_assistant/win/  Bug was also happening with software version 5.1.11 and 5.1.12, but since the keystrokes are showing up in the text chat interface in Minecraft, this does not appear to be an Elecom driver issue.

Video:

Demonstration and discussion of the bug can be seen at: https://www.youtube.com/watch?v=YcpjLtSvVqA