Loading code in Agda code blocks removes syntax highlighting from the Markdown text

[wolverian]

How to duplicate:

• Install agda, load agda2-mode
• Open a file Foo.lagda.md
• Write some Markdown and a fenced code block with agda language
• Load the Agda code with C-c C-l.
• Watch the Markdown highlighting disappear.

Not sure if this is an issue in polymode, poly-markdown or agda2-mode, but I thought to start here and try to find out where the issue is to see if I could help fixing it.