I can confirm that transcluded slices are not recognized.
However, I'm not entirely sure whether this sort of recursive evaluation
should be supported.
So I wouldn't consider this a bug - it's more of a feature request
(which doesn't make it irrelevant, so thanks for reporting this).
Could you raise a ticket:
http://trac.tiddlywiki.org
-- F.
Sorry, the link was broken - I've fixed that so it's pointing to the
correct location now:
http://trac.tiddlywiki.org/register
-- F.