How to reproduce:
1. Open project "case_1123066-HDRPLitUnlitNodes"
2. Open the "New Shader Graph 1" asset in Shader Graph
3. Create either a "HDRP/lit" or "HDRP/unlit" Master node
4. Try connecting the Color node to the Master node

Expected result: nodes can still be deleted, connected and the shader graph can be saved. There are no warnings or errors in the Console Window
Actual result: no node can be created, deleted or modified, nodes cling to the cursor when moved (follow the cursor when the left mouse button is up). Multiple error messages are visible in the Console Window. Shader Graph Window cannot be closed and Unity Editor is made unusable.

Reproducible with: 2019.1.0b2, 2019.2.0a4
Not reproducible with: 2018.3 (HDRP version 5.3.1 unavailible)

Reproducible with package version: 5.3.1
Not reproducible with package versions: 5.2.3 and older

Note: this only happens with these two nodes - other HDRP nodes such as "HDRP/Hair", or "HDRP/Fabric" etc. do not break editability.