Non-http URL schemes in Markdown cells

I use URLs like these to link to scientific papers in my Papers2 library:
`papers2://publication/citekey/Polsky:2004jc`

In the notebook, the following results in a clickable URL:

```
%%HTML
Polsky:2014jc
```

But in a Markdown cell, this doesn't work (link is underlined but nothing happens when clicked):

```
[Polsky:2004jc](papers2://publication/citekey/Polsky:2004jc)
```

Indeed the page source shows it was rendered as `Polsky:2004jc`. Changing the scheme to http causes a href attribute to appear (not fit for the original purpose obviously).

I tested it in the current version of `marked` and the link renders properly. Is that a security setting? The notebook is trusted.