System Information
Operating system: Windows-10-10.0.18362 64 Bits
{F7727044}Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 417.01

Blender Version
Broken: version: 2.81 (sub 8), branch: master, commit date: 2019-09-08 21:40, hash: rBf3a4f12ac090
Worked: (Blender 2.81 build September 04)

Short description of error
When the Bump node is placed in a node-group, bump is not working (as it should).

Exact steps for others to reproduce the error

1. Add a plane and give it a new material
2. Add: bump node and a texture. Noise for example.
3. Connect Noise texture (Fac) to height socket of bump node.
4. Connect the normal of the bump node (out) to the normal (in) of principled BSDF).

This works. But now;

5. Make a NodeGroup of the Bump node and the noise texture
6. Connect this nodegroup with the prinicpled shader (normal and optionally Base Color).

Now there is no bump, and if you adjust the strength strange things are going on with the normals.