A GitHub bug I recently noticed that seems related:

Expected: When a repo's readme is named `README` (without the `.md` suffix), it is rendered as plain text. When a repo's readme is named `README.md`, it is rendered as Markdown.

Actual: When a repo's readme is named `README` (without the `.md` suffix), the presence of `$` causes parts of the file to be rendered as math. For a real-life example, see the readme in https://github.com/idianal/personal-site.

Can someone please point me where I can submit a bug report/issue for this?