How to reproduce:
1. Open the attached "1306667_Repro" project
2. In the Project window double click on the "New Shader Graph" Asset to open the Shader Graph window
3. In the Shader Graph window select and delete the edge between "Position" Node and the "Position" input in the "Vertex" Node

Expected results: Only the edge is deleted
Actual results: The "Position" input in the "Vertex" Node block is deleted with the edge

Reproducible with: 10.1.0 (2020.2.0b12), 10.2.2 (2020.2.2f1, 2021.0b3, 2021.2.0a2)
Could not test with: 4.10.0-preview (2018.4.31f1), 7.5.2 (2019.4.18f1), 8.3.1 (2020.1.17f1) because the VFX Graph didn't have the Vertex Node block

Notes:
- The issue is reproducible on the Node blocks where nodes are not inserted by default, like "Vertex" in the VFX Shader Graph (for example in HDRP "Lit Shader Graph" the issue is not reproducible with the "Vertex" input Nodes as it has input Nodes created by default)