Inconsistent behavior of instance_eval

[k0kubun]

Related to: #3029

With current mruby master(501e1ef) and conf.gem core: 'mruby-eval', I got following behavior.

$ bin/mirb
> class A; def test; [''].each { p self }; end; end
 => :test
> A.new.test
#<A:0xdc55b0>
 => [""]
> A.new.instance_eval("test")
#<A:0xdc38d0>
 => [""]
> A.new.instance_eval("[''].each { p self }")
main
 => [""]

While I got main for the last result of p self, I think it should be #<A:....>. Is it interntional?