set_trace_func passes strange binding on method call ("call") if invoked method was defined by define_method. Correctly speaking, the caller's binding was passed.

example¶

class C
define_method(:foo){
p:foo
}

def bar
p:bar
end
end

set_trace_func(lambda{|ev, *args|
if ev == 'call'
p eval('self', args[3])
end
})
C.new.foo
#=> main
C.new.bar
#=> #<C:0x2bbc360>

On Ruby 1.8, there is no problem.