Copying a Symbol that has color variables for color overrides to another documents makes the color variables detach.
I’m not sure how clear that is, but it’s very easy to reproduce in all versions.
Create 1 color Variable. Create a rectangle with another random color. Turn that rectangle into a symbol. Override it’s color with the Color Variable. Copy and paste to another document. Color Variable has detached.
Somehow the Color Variable is still copied to the new document.
Bug is present if the Color Variable exists or not in the 2nd document.