Thanks for reporting your crash! By any chance could you provide more info on what happened?
Were you unable to back out of the controller settings after remapping your keys? If so, did you check if the newly mapped 'Jump/Back' key worked to get out?
The bug with the 'diff_name' variable is caused by an unrecognised difficulty setting; did you perhaps externally alter the difficulty level by accessing the config file and set it below 1 or above 8?