**System Information**
Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1050/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 417.22
**Blender Version**
Broken: version: 2.80 (sub 74), branch: master, commit date: 2019-06-19 18:29, hash: `rBd30f72dfd8ac`
Worked: (optional)
**Short description of error**
The mix factor in the Data Transfer modifier does not work when using Custom Normals option and a vertex group. It works if you aren't use a vertex group. I would expect the vertex group to act as a mask similar to the Vertex Weight Edit Modifier.
**Exact steps for others to reproduce the error**
1. With default cube add a vertex group with some weights on the vertices
2. Add a plane object
3. Add a Data Transfer modifier with the plane as the target
4. Turn on the options Face Corner Data and Custom Normals. Any loop mapping option other than Topology should work. I use the default.
5. Add the vertex group to the modifiers property
6. Trying to move the Mix Factor property does not effect the result at all.