visionmedia/mocha — comment on commit f0781afdad9da6ed34ebf55e1808d03b1cbeb6f6
File:  line 0
By jfirebaugh:

When you assign `mocha.run` as the event callback, when it gets called, the event object gets assigned to `Reporter`.

Never mind though, it's trivial to fix and the ability to supply a custom reporter is great.