Stories Lose Tasks?

Hello All, first post!

I have stories with child tasks in my planning tree which I have decided to remove from my current sprint and include in a later (unplanned) sprint.

When I have removed the stories the association with the child tasks seems to be lost as well so I now have tasks floating around with no parent. This happens both when I click 'remove' on the story card within the planning tree and also if I use a 'Back in to Backlog' transition.