How do you classify web archives?

Unlike page captures, web archives have a “Classify” button. However, when I click it the side window doesn’t contain anything. Normally, for text documents I get a list of possible groups, but not when the document is a web archive. Is this a bug, or non-feature? Can someone please help?

This is an update to my previous post. I’ve noticed that you don’t get groups in the classify panel only when web archives are created through applescript. If the web archive is created normally (by the contextual menu, for example) then you do get a list of groups to classify into. This seems to me like anomalous behaviour. Anyone would like to comment on this?

In this same (sort of) vein, my “Downloads” -> “Create Offline Archive” script seems to do nothing most of the time but occasionally works on a web page, even though the scripts in “Downloads” above the COA script seem to work OK. Anyone know what is going on?