Manual mapping of EMS USB2 under macOS Catalina

The EMS USB2 is an adapter from (up to two) PS2 dance mats to USB. It works under macOS Catalina on Stepmania Outfox without any drivers. I came up with the following Stepmania/Data/manualmapping.txt file to allow use of both dance mats, 6 buttons on each. However, I’m wondering if I did this right, since it has to map the arrows for one player to the ABXY buttons.

03000000430b00000300000012190000,EMS USB2 dual joystick,dpdown:b29,dpleft:b31,dpright:b27,dpup:b25,back:b17,start:b19,leftshoulder:b16,rightshoulder:b18,a:b28,b:b30,x:b26,y:b24,platform:Mac OS X,

There’s something weird about the ABXY buttons so I changed my mapping to use other parts of the controller and it works better now:
03000000430b00000300000012190000,EMS USB2 Order,leftshoulder:b16,back:b17,rightshoulder:b18,start:b19,leftstick:b24,dpup:b25,rightstick:b26,dpright:b27,lefttrigger:b28,dpdown:b29,righttrigger:b30,dpleft:b31,platform:Mac OS X,

Every time I quit or save/reload keymap.ini to disk, the ABXY buttons were turning into ‘unknown’. This updated mapping is a workaround.

The issue with button mappings changing to unknown should be fixed in the latest alpha (4.5.8). I used to have the same issue but, after remapping my ABYX buttons after updating to 4.5.8, the issue has not reoccured. Maybe this would also be the case for you?