When you have a misbehaving callback, you can add a warn in active_support/callback.rb in make_lambda(filter).
Someday maybe I'll make a gem to do this, but I just changed it to
when Symbol
lambda { |target, _, &blk| warn "Running symbol callback #{filter}"; target.send filter, &blk }
when String
l = eval "lambda { |value| warn \"Running eval callback #{filter}\"; #{filter} }"