Node reference fields within fieldgroups ignore DS settings

I'm reporting this here because I spent at least two hours to figure it out, and if it helps somebody else save some time, so much for the better.

Here's what happened:
I have a content type Product and a content type Author. In the product full node I was showing the teaser for Author.

To make things cleaner in the backend, I moved the Author node reference field inside of a fieldgroup in the Product node. This caused the DS node reference field to stop working. It took me a while to realize it because I didn't check the full node display when I move the field inside of a fieldgroup.

My solution was to pull the field back out of the fieldgroup.
Hope this helps somebody else who stumbles here.