so it turns out caching Gem.dir is a terrible idea

lib/bundler/rubygems_integration.rb

@@ -3,11 +3,6 @@ class RubygemsIntegration
     def initialize
       # Work around a RubyGems bug
       configuration
-
-      # Cache Gem.dir and Gem.bindir because Rubygems 1.8 treats them as globals,
-      # changing them anytime you use Gem::Installer#install.
-      gem_dir
-      gem_bindir
     end
 
     def loaded_specs(name)
@@ -51,24 +46,19 @@ def sources
     end
 
     def gem_dir
-      # We cache this because Rubygems 1.8 changes Gem.dir every time
-      # a gem is installed, and we need the original.
-      @gem_dir ||= Gem.dir
+      Gem.dir
     end
 
     def gem_bindir
-      # We cache this for the same reason we cache gem_dir.
-      @gem_bindir ||= Gem.bindir
+      Gem.bindir
     end
 
     def user_home
       Gem.user_home
     end
 
     def gem_path
-      # Make sure that Gem.path is an array of Strings, not some
-      # internal Rubygems object
-      Gem.path.map { |x| x.to_s }
+      Gem.path
     end
 
     def marshal_spec_dir