Does this issue occur when all extensions are disabled?: Yes/No

• VS Code Version: github.dev
• OS Version: Windows 10

Steps to Reproduce:

1. Visit https://github.dev/lostintangent/python-tuples
2. Select any of the markdown cells
3. 🐛 breadcrumb preview says 'empty cell', this is apparently because the cell headers are created with HTML; if I rewrite them to be Markdown the breadcrumbs are accurate