[Backport 4.1] Variables in hst:parameternames don't work on multi-channel sites

See also Google Groups Discussion
A bit of setup before I get to the question, please bear with me.
 
Let's say our hst:configuration looks something like this:
 

• common
• sitemap
• commonurl
• hst:parametername : someparam
• hst:parametervalue : ${scope}

• dutch (inherits from common)
• sitemap
• dutchurl
• hst:parametername : someparam
• hst:parametervalue : ${scope}

• germany (inherits from common)
• sitemap
• germanyurl
• hst:parametername : someparam
• hst:parametervalue : ${scope}

 
we've set our sites up with hst:parametername: "scope" and values "dutch" and "germany" respectively.
 
When we go to the dutchurl when in the dutch site, the "someparam" is as expected "dutch"
Similarly when going to the germanyurl in the german site, the "someparam" is "germany".
 
However when we go to the commonurl within the dutch site, the "someparam" is "germany", same when we visit that url via the german site.
 
Is there a reason for this behaviour? I would have expected it to use the scope parameter from the site it entered, or nothing at all. but somehow it seems to pick one site at random, and runs with it.
 
Regards,
Martijn van der Vorst