My Environment

Expected Behaviour

When I use this markdown, I should get unique IDs on the headings:

## Heading

<div markdown="1">

## Heading

</div>

Expected output:

<h2 id="heading">Heading</h2>
<div>
  <h2 id="heading-1">Heading</h2>
</div>

Current Behavior

However, I get duplicate IDs:

<h2 id="heading">Heading</h2>
<div>
  <h2 id="heading">Heading</h2>
</div>

At first, I thought this was a kramdown bug, but when I use kramdown directly from the command line, I get the expected unique IDs. This suggests that the bug is happening in the Jekyll context.

This happens with kramdown 1.17 and 2.1, and in both Jekyll 3.8.6 and 4.0.0 on Windows and Ubuntu.