Mocking 'each' method with yields/multiple_yields behaves incorrectly under JRuby

I get different results under JRuby (1.5.6 but also seen under 1.5.2) and MRI for this. Using the latest mocha (0.9.12).

jruby :001 > require 'mocha'; o = Object.new; o.extend Enumerable; o.stubs(:each).multiple_yields(1,2); p o.to_a
[[1], [2]]

whereas this is what I see as being the correct behaviour under MRI:

ruby-1.8.7-p302 :001 > require 'mocha'; o = Object.new; o.extend Enumerable; o.stubs(:each).multiple_yields(1,2); p o.to_a
[1, 2]

The difference is visible via other enumerable methods too (map, select, etc), but, interestingly, not when calling 'each' directly. So eg o.each {|x| p x} has different output to o.map {|x| p x}.

I wasn't able to replicate the problem using other methods of stubbing the each method, only with mocha. Possibly a somewhat strange interaction between Mocha's magic and slight differences in the under-the-hood Enumerable implementations between these ruby platforms.

Would be good if this could either be fixed or worked around in mocha, or if it's actually a JRuby bug, pinned down and replicated without mocha so it can be reported to JRuby or a test case added to rubyspec.