Apache reverse proxy to application on tomcat with 8080 port gives wrong URL in response header

I have Apache (2.2) server with below configuration for reverse proxy to application running on tomcat(6) on 8080 port.

....  
ServerName ext-domain  
ProxyPreserveHost On  
ProxyPass  /myapp http://int-domain:8080/myapp  
ProxyPassReverse /myapp http://int-domain:8080/myapp  
....  

When I access below URL from browser

"http://ext-domain/myapp"  

I get below URL replaced in browser address bar.

"http://ext-domain:8080/myapp"  

And apache access log says…

"GET /myapp HTTP/1.1" 302 421 "-" "Mozilla/5.0"...    

How to avoid this port 8080 insertion in response URL?
Can someone help on this? thanks.