Caching in tac_db_rewrite_sql results in duplicate tags for freetaging vocabularies

In taxonomy_access_module_db_rewrite_sql, a static variable $taxonomy_access_sql_clause is used to save the first evaluation of the visible terms for the user. There is no mechanism for that cache to be invalidated if new terms are added or term_access or term_access_default change between requests. This can result in duplication of tags when multiple nodes are saved with a new tag, since the tag did not exist at the first evaluation, it is not visible for the duration of the request. So each node adds a new copy of the same tag name.

This issue manifest itself with image_upload when the image type has a tagged vocabulary and the user does not have "administer taxonomy" and inserts multiple images with a new tag.

Unfortunately, taxonomy_node_save does not call db_rewrite_sql when it inserts a new tag, so there is not a chance to invalidate the cache at that point. The workaround for my application, is to remove the static declaration and not cache at all.

MySQL 5.1, though, I do not believe it matters.