Apologies if my analysis is wrong on this one, but I've spent a couple hours on it thus far. I have a Rails 3.2 application that uses rspec. I load rspec up in a lib/tasks/rspec.rake file as is customary. In JRuby 184.108.40.206 this works just fine, but in JRuby 1.7, minitest's spec task always takes precedent. I assume Rails is loading this up some place as I don't have test-unit anywhere in my code or Gemfile.
I've tried both with and without invoke dynamic enabled. In both cases minitest's spec task takes precedence. What's really odd is the "rake -T" output includes my description strings, indicating rake thinks my tasks are the ones to use.