URL-Generator multiple http headers with the same name

Hi There,
I'm using the url-generator to do an http get request in which I would like to pass some additional headers under the same name. So the config of my processor looks like this:

<config>
   <url>http://someurl</url>
   <header>
      <name>query-field</name>
      <value>a</value>
   </header>
   <header>
      <name>query-field</name>
      <value>b</value>
   </header>
   <header>
      <name>query-field</name>
      <value>c</value>
   </header>
</config>

Now it seems that the eventual request only contains one http header under the name of 'query-field' with c as its' value. Could you tell me whether this is a bug or that this is conform spec/design?

TIA,
Jasper Linthorst