Issue with Zuiki Mascon Switch Controller - Proton interprets the absence of a right stick as meaning the right stick is pointing continually to the left

[eldomtom2]

I am having an issue using the Zuiki Mascon Switch Controller with the game Train Crew (steam id 1618290). The Zuiki Mascon is a specialised controller designed to imitate the controls of a train. It lacks a right stick. Train Crew is programmed to support this controller natively without the use of Steam Input. The controller is recognised by Steam and the game, and in most regards works fine. However, Proton seemingly interprets the absent right stick as continually pointing fully to the left.
I can fix this problem by editing the prefix registry and creating a DWORD named "Map Controllers" in HKLM\System\CurrentControlSet\Services\winebus and setting it to 0, but this creates a new problem. It now interprets the centre of the left stick as being fully up. Moving the left stick down is interpreted as moving the stick through the full range of movement (i.e. slightly down is interpreted as slightly up and fully down is interpreted as fully down). Moving the left stick upwards leads to it being interpreted as pointing fully down regardless of position until it is moved back to the centre - it seems like the controller being moved "above fully up" causes it to loop around and become fully down.
I am using Proton Experimental.