Header in first line didn't highlight properly

I have a markdown file that starts like this:

```
## 3D buildings 0.1

A 3D model (not just outline plus height) of buildings and other physical features, used for planning, architecture and communicating proposed construction.

#### Recommended format
3DS

...
```

Opening it in MacDown looks like this:


Scrolling up past the top of the document makes it highlight properly.

Open the supplied Markdown document in MacDown and reproduce the initial rendering before and after scrolling above the document. The issue is done when the first-line heading highlights correctly immediately on opening, without needing to scroll.

Written by the indexing model from the issue text.