This is not a bug. Downvotes on questions have been "free" to the user who casts them for quite some time (at least since May 12 of 2011). That means that you will not lose reputation points for downvoting questions, however the user who owns that question will still lose reputation posts as a result of the downvote.
The hope was that this would encourage users to cast more downvotes on poor quality questions without worrying about sacrificing their own hard-earned reputation. As the statistics show, our hopes were correct and this plan worked as expected.
Downvoting answers does still cost reputation points for both the person who casts the vote and the person who owns the post. This has not changed.