'rake routes' modifies vendor/plugins/haml/init.rb

I'm getting a strange and annoying bug when I run rake routes on a rails project. Every time it for some reason modifies the file vendor/plugins/haml/init.rb. Here's the diff:

-# Load Haml and Sass.
+# Load Haml

Using rails version 2.3.4 and my vendored version of Haml is 2.2.23. I've got a couple of other versions of rails (3.0.7, 3.0.4, 3.0.3) and haml (3.1.2, 3.1.1, 3.0.25), along with haml-rails (0.开发者_如何学编程3.4). The bug pops up with rake routes as well as rake db: commands, but not rake stats. Any ideas?

Starting from version 3.0.22 haml doesn't include sass anymore. You need to install sass gem separately or use haml older than version 3.0.22.

Well, uninstalling the haml gem from my gemset fixed it, such that it just uses the vendored version. Not sure why the gem version would alter the vendored version, though. It also works fine if I install the the same gem version as what is in the vendor directory.