Attempt to move the task using the context menu
In the attached demo project, this shows the insert and removes are reflected in the Gantt on the right, but not in the Grid on the left. If you insert a breakpoint, and look at the underlying ViewModel, the ViewModel itself is correct.
Steps to reproduce:
1) Select Task 2.2
2) Right-click, and select "Move" from the context menu
3) Select Task 1
4) Right-click, and select "Drop Below"
The Gantt is correct. The ViewModel is correct. The Grid is missing Task 2.2.