diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index 22372b4d8a2b6..e332c9b110974 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,5 +1,7 @@
 *1.12.1* (April 6th, 2005)
 
+* Fixed that template extensions would be cached development mode #4624 [Stefan Kaes]
+
 * Update to Prototype 1.5.0_rc0 [Sam Stephenson]
 
 * Honor skipping filters conditionally for only certain actions even when the parent class sets that filter to conditionally be executed only for the same actions. #4522 [Marcel Molina Jr.]
diff --git a/actionpack/lib/action_view/base.rb b/actionpack/lib/action_view/base.rb
index 3e73159d266c5..2ee4227a6f754 100644
--- a/actionpack/lib/action_view/base.rb
+++ b/actionpack/lib/action_view/base.rb
@@ -157,6 +157,11 @@ class Base
     @@cache_template_loading = false
     cattr_accessor :cache_template_loading
 
+    # Specify whether file extension lookup should be cached.
+    # Should be +false+ for development environments. Defaults to +true+.
+    @@cache_template_extensions = true
+    cattr_accessor :cache_template_extensions
+
     # Specify whether local_assigns should be able to use string keys.
     # Defaults to +true+. String keys are deprecated and will be removed
     # shortly.
@@ -312,15 +317,11 @@ def compile_and_render_template(extension, template = nil, file_path = nil, loca
     end
 
     def pick_template_extension(template_path)#:nodoc:
-      @@cached_template_extension[template_path] ||=
-        if match = delegate_template_exists?(template_path)
-          match.first.to_sym
-        elsif erb_template_exists?(template_path):        :rhtml
-        elsif builder_template_exists?(template_path):    :rxml
-        elsif javascript_template_exists?(template_path): :rjs
-        else
-          raise ActionViewError, "No rhtml, rxml, rjs or delegate template found for #{template_path}"
-        end
+      if @@cache_template_extensions
+        @@cached_template_extension[template_path] ||= find_template_extension_for(template_path)
+      else
+        find_template_extension_for(template_path)
+      end
     end
 
     def delegate_template_exists?(template_path)#:nodoc:
@@ -345,7 +346,7 @@ def file_exists?(template_path)#:nodoc:
       if template_file_extension
         template_exists?(template_file_name, template_file_extension)
       else
-        @@cached_template_extension[template_path] ||
+        cached_template_extension(template_path) ||
            %w(erb builder javascript delegate).any? do |template_type| 
              send("#{template_type}_template_exists?", template_path)
            end
@@ -371,6 +372,21 @@ def path_and_extension(template_path)
         template_path_without_extension = template_path.sub(/\.(\w+)$/, '')
         [ template_path_without_extension, $1 ]
       end
+      
+      def cached_template_extension(template_path)
+        @@cache_template_extensions && @@cached_template_extension[template_path]
+      end      
+          
+      def find_template_extension_for(template_path)
+        if match = delegate_template_exists?(template_path)
+          match.first.to_sym
+        elsif erb_template_exists?(template_path):        :rhtml
+        elsif builder_template_exists?(template_path):    :rxml
+        elsif javascript_template_exists?(template_path): :rjs
+        else
+          raise ActionViewError, "No rhtml, rxml, rjs or delegate template found for #{template_path}"
+        end
+      end
 
       # This method reads a template file.
       def read_template_file(template_path, extension)
diff --git a/railties/environments/development.rb b/railties/environments/development.rb
index cbd8529e6c4fe..0589aa979e30b 100644
--- a/railties/environments/development.rb
+++ b/railties/environments/development.rb
@@ -14,6 +14,7 @@
 # Show full error reports and disable caching
 config.action_controller.consider_all_requests_local = true
 config.action_controller.perform_caching             = false
+config.action_view.cache_template_extensions         = false
 config.action_view.debug_rjs                         = true
 
 # Don't care if the mailer can't send