See ##40867 for the full picture.

The computation of the derived values for the parent must be triggered when:

* [x] "work" field is changed
* [x] "remaining work" field is changed
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion "% complete" field is changed
* Begin of the insertion[x]End of the insertion Begin of the deletion [ ]End of the deletion "status" is changed
* [x] a child is created
* [x] a child is deleted
* [x] a child is added (indent hierarchy)
* [x] a child is removed (unindent hierarchy)

Then the update propagates up to all the ancestors.