Problem with headers numbering in HTML output

[ghost]

$ pandoc --version
pandoc 1.11
$ cat test.md
% Title
% Author
% Date

Header
======

$ pandoc --from markdown --to html5 --standalone --toc --self-contained --number-sections --output test.html test.md

The HTML result has a toc and numbered headers, as expected, but there's a numbering problem:

Title
Author
Date
    1 Header
2 Header

I.e. the numbering starts at 1 on the ToC but starts at 2 in the body.