Ah! That's the case in which a shot says more than hundred words!
That's weird indeed. The "elements" of F4 HUD are on \RailSimulatorCore folder and are used in the same way by all engines (of same type: diesel, steam or eletric). Maybe this is one of those default core files corrupted. To be sure if this is your case load a scenario with any other diesel engine and see if the F4 HUD is missing controls also. Also check with the GP-38 if you can drive by keyboard, and let me know. And then, maybe, I can show a fix for it.

Who doesn't have dog, hunts with cat.