Ranking with subtasks incorrectly updates the board

Something in the data model is incorrectly updated. Subsequent parent rank operations place the parent at the wrong location. This might also be the source for rogue board updated messages showing up.

How to reproduce
1. Rank a parent (having a subtask) to the last position
2. Rank another issue at the end

Outcome: The issue is placed between the parent and its subs.
Expected: The issue is placed after the subs