Encoding problem with HttpParameters in Struts2

Question

I have problem with HttpParameters from Struts2. When i send the form with HTTP POST, the parameters are correctly encoded. After the form is submitted, there's a button to go back. When i press it, it sends a HTTP GET request, but the encoding is different. For example, if i write München, the parameter will change to München..Everything in my project is encoded with UTF-8 and i'm guessing it has something to do with Struts2.

Questions:

1. How does the encoding change?
2. Where is the value of HttpParameters saved?

import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;
import com.opensymphony.xwork2.Preparable;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;


import org.apache.struts2.ServletActionContext;
import org.apache.struts2.dispatcher.HttpParameters;
import org.apache.struts2.interceptor.HttpParametersAware;

public abstract class BaseAction extends ActionSupport implements Preparable, ModelDriven, HttpParametersAware {

    private HttpParameters httpFormParams;

    protected void init(DBConnection conn, 
            Object formBean,
            HttpServletRequest request,
            HttpServletResponse response)
    throws Exception {
    }

    public void setParameters(HttpParameters parameters) {
        this.httpFormParams = parameters;

    }

    public HttpParameters getParameters() {
        return this.httpFormParams;
    }

}