Repro Steps:
- create a new project that uses ShaderGraph
- make a new shader
- Create a new Colour node and connect it to the Colour Master input filed
- notice that the default colour filed still remains

Or:
- Download this project
- Open the "gr" shader
- Create a new Colour node and connect it to the Colour Master input filed
- notice that the default colour filed still remains

Cannot repro in 2019.1.0b7 or 2019.2.0a7
Reproduced with 2019.2.0a8 and trunk (2019.2.0a9)