JabRef has internally a field marker that marks a field as Markdown. org.jabref.model.entry.field.FieldProperty#MARKDOWN

When that field is rendered in the preview, {} should be kept.

Example content of a Comment:

# test

{ test }

```javascript
function hero() {
}
```

This issue is more about code reading and understanding JabRef's archictecture. The "real" fix should be a few lines of code: Checking for the field property MARKDOWN and passing the field value with plain latex (and not latex free).