Here is one thing you could try:
Go to the "Saved Games\DCS BlackShark 2\Config\Input\ka-50\joystick" folder (in the your home folder) and delete the file for the throttle. There are also folders for "Default" and "ka-50_easy" for which you could proceed in the same way.
Afaik, this should remove any knowledge of BS2 on the throttle.
I have no idea whether this works for you--it worked for me when I had edited this bindings file for my switchboard and some commands had become unassignable. However, these unassignable commands were easily distinguishable and non-clickable in the options menu.