Hi,
We have noticed an inconsistency in the UI around establishing dependencies and parent/child validation. If the schedule has a simple parent/child relationship (where the child is the leaf) and both are marked as manually scheduled, it is not possible to associate the child to the parent as a predecessor (i.e. this works as intended). We've verified this isn't possible by either manually typing in the parent Id in the grid, or by trying to add it in the Edit Task modal.
However you can select both tasks, right-click and select "Add Dependencies" and this validation appears to be skipped. I've tested in this in the advanced demo and verified this behaviour there as well.
Is this intentional?