How to reproduce:
1. Create LWRP project
2. In Project window, create and open a PBR Shader (works with any shader)
3. In the "Shader Graph" window's, hover over the Blackboard corner

Expected result: the cursor changes to the resize cursor
Actual result: the cursor sprite does not change to resize cursor but you are still able to resize the window

Reproducible with: 2018.3.0b1(LWRP - 3.3.0-preview, ShaderGraph - 4.10.0), 2019.3.0a6 (LWRP - 5.1.0, Shader Graph - 5.1.0), 2019.3.0a3 (LWRP - 6.5.3, Shader Graph - 6.5.3)