I'm on an Xbox Series X and use a controller with back buttons. I have jump bound to "Down on the D-Pad" (which is what my back button is also bound to). When I'm on Kepler and use the Matterspark, I can not jump with the custom binding I had, it automatically reverts the jump button to the default "A" button. The boost ability on Matterspark however, still uses my custom binding of "Up on the D-Pad" (my other back button). I also have my Vehicle Boost button as "Up on the D-Pad" so I assume that's where that is coming from. Before the Ash and Iron update my custom binding worked for jumping the Matterspark. All other custom bindings still work. It's only in Matterspark that I've found this.