I have been busy with other things in my life lately, so I haven't been active on MSE for the last couple of days. First my reputation decreased by 2 points few days ago, and today when I checked my profile again my reputation had decreased by another 8 points. I checked the reputation tab and it didn't show any downvotes or changes in my reputation. How is that possible?
The loss of reputation appears to be due to the (in this case automatic) deletion of questions on math.SE.
When a question (or any post, really) is deleted, all up- and down-votes associated with that post (and all associated changes in reputation) are also removed. Also, reputation earned by editing such posts are removed.