Only affects 1.7. Reproduction can be found at https://github.com/samphippen/playground.git under call_origin_with_module. bundle install, then bundle exec ruby explain_the_bug.rb.

JRuby 9k and MRI:

$ bundle exec ruby explain_the_bug.rb 
uri:classloader:/jruby/kernel/kernel.rb:17: warning: unsupported exec option: close_others
Pure module singleton class owner #<Class:#<Module:0x77847718>>
Pure module singleton class owner equals singleton class? true
jrjackson singleton class owner #<Class:JrJackson::Raw>
jrjackson singleton class owner equals singleton class? true

JRuby 1.7.x:

$ bundle exec ruby explain_the_bug.rb 
Pure module singleton class owner #<Class:#<Module:0x795cd85e>>
Pure module singleton class owner equals singleton class? true
jrjackson singleton class owner JrJackson::Raw
jrjackson singleton class owner equals singleton class? false

Cause of rspec/rspec-mocks#964. Thanks @samphippen for the repro case.

I suspect this is a problem of divergent logic in the reflective JRubyMethod annotation binding. The jrjackson gem has a JRuby ext component, which would use the reflective logic. I could not reproduce with exts shipped with JRuby, and they all use our generated "Populator" code. I also fixed a number of discrepancies between the generated populators and the reflective populators for JRuby 9k while looking into pure-invokedynamic method objects. Somewhere in there is a fix we need to backport to 1.7.