Fenced language highlighting is overriden when reopening hidden buffer

[ChooZ-B]

On reopen of a hidden buffer and after pressing enter in the Toc-window to move to the corresponding heading the
syntax highlighting of language code blocks changes to the default markdown code block color as specified in the syntax file.
Calling MarkdownHighlightSources() with the force option also only removes the syntax highlighting within the code blocks but does not restore the desired syntax.

MWE:

```c
for (;;) {
   foo;
}
```

My settings for the code blocks in this case are as follows:

vim.g.vim_markdown_fenced_languages = {'c'}
vim.g.vim_markdown_conceal_code_blocks = 0

I'm using neovim 0.10.4 without any additional plugins.