TOC not rendered when set `markup: pandoc` in front matter

[Sollovin]

Hello, I want to use pandoc to render math eqs in my post, so I add markup: pandoc in the front matter. But, it seemed that the TOC would not be rendered correctly.

A minimal post file that could reproduce that phenomenon could be:

---
title: "Test"
date: 2019-10-30T21:29:33+08:00
toc: true
draft: true
markup: pandoc
tag:
  - untagged
---

# Heading 1

# Heading 2

which shows as: