How to reproduce:
1. Create a new Unity project
2. Download the ShaderGraph package
3. Create a PBR Graph and add several property nodes
4. Connect them to the Master node
5. Select all nodes, right-click and select 'Convert To Sub-Graph'
6. Open the newly generated Sub-Graph

Expected result: property nodes are not stacked in one position
Actual result: property nodes are stacked in once position

Reproducible with: 2018.4.1f1, 2019.1.4f1, 2019.2.0b4, 2019.3.0a4
Could not test with: 2017.4.27f1(ShaderGraph not available)

Reproducible with package versions: 1.1.2 preview, 6.7.1
Could not test with package versions: 0.1.8 preview - 1.1.1 preview(incompatible with the versions tested)