Converting an enum field between a constant and a variable removes editable field

Steps to reproduce:

1. Download and import the attached "gtk-convert-enum-constant.unitypackage"
2. Open "New Graph"
3. Drag a wire from the "Enum variable" port and drop on an empty space on the canvas
4. Select "Create Variable (of port type)"
5. Convert the enum variable node to a constant
6. Convert the constant to a variable
7. Convert the variable once more to a constant

Actual results: The constant node is missing the fields

Expected results: The constant node is displays the fields

Tested on (OS): MacOS