all tag cloud blocks show the same vocabulary

Problem/Motivation

in a site with multiple vocabularies, a block is provided for each but they all show the same tag cloud for the first vocabulary (Tag, by default). at the URL /tagclouds/chunk/[name of other vocab] the proper tag cloud is visible. but only the Tag vocabulary appears in all blocks.

Steps to reproduce

create at least two vocabularies.
add fields for the vocabularies to a content type.
place tag cloud blocks for each vocabulary.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes