I recently downvoted a poorly written question. The downvote was registered on the question, the change in reputation was documented on the user's page, the downvote count on my profile incremented, but I did not lose any reputation. Anytime I have downvoted in the past, the reputation change happened within 5 minutes, but it has been some time now and I have not seen any change. I have also received an upvote since then and that has registered fine.
Any ideas on why the downvote was not calculated into my total?