The same thing happened to me, and I realized it was because I was following a curation trail which also upvoted my post, so it appears as though you are the one upvoting your own post.
Congratulations on hitting the top 15! That's huge all things considered :)
Thanks.
Yes, I suspect the @newbieresteemday curation trail of being guilty. I can't put them to trial yet, because I haven't taken the time to look into it, but it is the prime suspect. π
Not that it matters that much. Just two weeks ago I was self-voting on all my posts...
haha @simplymike, we do what we do!