Footnotes with "w" in the anchor don't render as footnotes!

When writing GFM with footnotes, only footnotes that have anchor text that does NOT include the letter "w" get rendered. Anchors like "a", "hello", and "testing-this" will render properly; anchors like "w", "awesome", and "not-without-a-sense-of-humor" will not render properly.

The following text demonstrates the problem:

Footnotes are only recognised sometimes.¹

The problem seems to be when there's a w in the footnote anchor.²

Anchors without w seem to render OK. It's just those with w that get ignored.^{3 4 5 6 7}

Here's how that renders in Firefox on Linux:

Here's the text quoted, so you can see the source code:

Footnotes are only recognised sometimes.[^like-this]

The problem seems to be when there's a w in the footnote anchor.[^w]

Anchors without w seem to render OK. It's just those with w that get ignored.[^a] [^w2] [^a2] [^this-is-not-awesome] [^this-is-not-rad]

  [^like-this]: Like this.
  
  [^w]: This won't be rendered.
  
  [^a]: This will be rendered.
  
  [^w2]: This won't be rendered.
  
  [^a2]: This will be rendered.
  
  [^this-is-not-awesome]: This will not be rendered.
  
  [^this-is-not-rad]: This will be rendered.

1. Like this. ↩

2. This won't be rendered. ↩

3. This will be rendered. ↩

4. This won't be rendered. ↩

5. This will be rendered. ↩

6. This will not be rendered. ↩

7. This will be rendered. ↩