incompatible with activesupport somehow

[godfat]

Found this incompatibility when using dm-core (gem) with heroku (gem),
and heroku is depending on activesupport (it should really just pick
a json gem, instead of using activesupport), and then our app stopped
working... Here's the minimal program to reproduce the problem.

Sorry I don't have time to dig into this, hope this minimal program
is enough to find out the problem. Thanks a lot!!

https://gist.github.com/894330