MVC :: Why Do Route Values Not Get The New Value

When I do an Html.RenderAction( action, controller, new { varName = value } ); if the original request had a parameter equal to varName, then the value is not changed in a render action.

Example:

1. Post to "C1/A1" with a string var _test = "abc"

2. Inside C1/A1 get some data and return a partial view

3. Inside the partial view I invoke an action on another controller. The action has an input variable with the same name and type (string _test) Html.RenderAction( "A2","C2", new {_test="fgh"});

4. the value in _test that arrives at C2/A2 is still "abc"

I've traced through it step by step, and the value used in the view render action call is correct, but in the next trace step, the value received at C2/A2 is incorrect.

If this is not an error, and creating a new route value to pass in render action is not the correct way to handle this, what is?