[MapProxy] problems with setting http headers

[Oliver Christen]

dear all

im using MapProxy 1.6.0a 20130115

im having a problem with configuring http headers parameters for a source,
the parameters are getting injected into the request url instead of in 
the http headers:

sources:
   MyLayerWMS:
     type: wms
     req:
       url: 'http://*targetserver*/wms/?'
       layers: MyLayer
       http:
         headers:
           Cache-Control: no-cache
           test: foo3

the request is seen like this on the target server:

/wms/?styles=&http=%7B%27headers%27%3A+%7B%27test%27%3A+%27foo3%27,+%27Cache-Control%27%3A+%27no-cache%27%7D%7D&format=image%2Fpng&height=1104&bbox=420000.0,30000.0,696000.0,306000.0&layers=PointsHotel&service=WMS&srs=EPSG%3A21781&request=GetMap&width=1104&version=1.1.1

im not sure that 
"http=%7B%27headers%27%3A+%7B%27test%27%3A+%27foo3%27,+%27Cache-Control%27%3A+%27no-cache%27%7D%7D" 
is really correct there.

any idea why im getting such strange result?
maybe I didnt understand the usage of  the "headers" config ?

thank you for any help you may provide

best regards
Oliver

-- 
Camptocamp SA
Oliver Christen
PSE A
CH-1015 Lausanne

www.camptocamp.com