FillOutAttributes Incorrect Task State

I have reproduced some incorrect/unexpected task system behavior reported by an outside user: a FillOutAttributes task is being set to the completable state when its dependency task is marked completed.

1. Load Test Project

To reproduce the issue, first load this project into modelbuilder: task-dependency.tgz

As shown in the first screenshot, the project has 3 tasks

1. Plain Task -- an smtk::task::Task instance. Its initial task state is completable.
2. Assign Attribute Resource -- an smtk::task::GatherResources instance that is used to connect the project's attribute resource to the third task. Its initial task state is completable.
3. Edit Attributes -- an smtk::task::FillOutAttributes instance for editing an "Elasticity" attribute in the project's attribute resource. Its initial state is unavailable because (i) its attribute resource has not been set via the Assign Attribute Resource task and (ii) there is a strict dependency on the Plain Task which is not completed.

2. Reproduce Incorrect Behavior.

In the Tasks View:

1. Change the "Assign Attribute Resource" task to the completed state.
2. Change the "Plain Task" to the completed state.
3. Note that the "Edit Attributes" task has changed to the completable state.
4. In the "Edit Attributes" controls, select Work on this to update the Attribute Editor.
5. Note that there is an invalid entry (Young's Modulus) in the attribute editor, which is inconsistent with the completable task state. The expected behavior is for the task to be incomplete when its attribute(s) is/are invalid.