Comma-separated font-family declaration split onto multiple lines

Hi there! I'm encountering a weird issue that I cannot really pinpoint.

The setup is as follows:

:root {
  --fontMain: "Open Sans", sans-serif;
}

body {
  font-family: var(--fontMain);
}

After running PostCSS (for which I have gulp setup, I run PostCSS-custom-properties with default settings), the resulting CSS is this:

:root {
  --fontMain:"Open Sans",sans-serif;
}
/* Notice the weird spacing of the first font-family property in body: */
body {
  font-family:"Open Sans"
,
sans-serif;
  font-family:var(--fontMain);
}

I believe this should work in the browser, and a minifier further down the line will probably solve it, but this seems weird behaviour to me. Any idea what causes this? Disabling all other postCSS plugins yields the same result.

postcss / postcss-custom-properties

Comma-separated font-family declaration split onto multiple lines #221