Cognito Pre-Signup Lambda trigger not being called on ForgotPassword

The docs for the Cognito ForgotPassword API call say that Lambda triggers for pre-signup, custom message, and user migration will be invoked. I have a pre-signup trigger that works as expected on the SignUp action, but it is not being called when I submit a ForgotPassword action. [These docs] show trigger source values for CustomMessage_ForgotPassword and UserMigration_ForgotPassword, but there is no PreSignUp_ForgotPassword or similar. Is this a bug? Thank you!