Hi all:
I’m having the same problem with these flying heartlings. It does seem to happen when someone else mine below them. I was able to save a few of them by calling them to arms, but this one didn’t seem to want to move from there, so I had to build a ladder directly to her.
Here’s a screenshot (URL, since I’m new):
(http://i.imgur.com/ktfAnzO.jpg)
http://i.imgur.com/ktfAnzO.jpg
Regards.