Windows 8.1, nvidia Geforce 920M
Broken: (2.79, 5bd8ac9)
Short description of error
This is a follow-up for bug #T53991
The driver for "ScaleX" does not update when "Driver Source" is altered
As stated by Sergey, it has something to do with "Depsgraph missing updates"
Exact steps for others to reproduce the error
Add a cycles material, create a driver in the node editor that takes input from any node variable within that material that uses the new dependency graph.
Attached example is attempting to control ScaleX using the variable input node, using the dependency graph.