@raeoks would you mind trying to target jruby-1_7 so that this is fixed in JRuby 1.7.x as well?
... don't think test should be added under test/mri as those might conflict when the MRI suite is merged

@eregon since its mostly your work-around ... any thoughts on getting those in?

These tests would be useful in RubySpec. You can just do a separate commit touching spec/ruby.

Well, if this behavior must be supported, I'd say there is not much choice.

I'll move test cases from test/mri/date/test_date_arith.rb to spec/ruby/library/date's add_month_spec.rb and next_year_spec.rb files.
Also I'll be start working on creating a new pull request to fix same issue on jruby-1_7.

The changes look ok to me but I defer to @eregon on when and whether this should merge.

@raeoks Could you move the test cases to specs? Or should I do it?

@eregon I'll do it and doing it right now.

@eregon Should I create a new pull request resolving #2867 for Jruby 1.7?

I guess yes but better ask @kares.
@raeoks Is this PR ready to be merged?

optimally, there would be only one PR targeting jruby-1_7 (branch is periodically merged to master) ...

I applied the commits to 1.7, 1.9-mode (1.8 Date is just so different and should not be affected the same way by this bug): 40e9140 and ec80a32.

I guess the merge in this case would not work so well (date.rb moved quite a bit), so I'd rather merge #3157 in master instead.