Fenced code block is not drawn correctly if filetype is set after a file is read

[hiecaq]

Setup to produce (with a vim / neovim that only has vim-markdown installed) and NORC:

1. save the following code as a file named test:

test

```c
int main() {
    int x;
    return x;
}
```

test

2. open the file with vim test.

3. :set ft=markdown. You'll see that the fenced block is not hightlighted with C's syntax immediately. Wait for a while / do something else randomly might fix it, but sometimes it never got redrawn with C's highlight.

[joemrt]

This problem still persists for me. Are there any updates on this or does someone know of a workaround?