Rounded dark theme white outline

[Ingolf]

macOS, latest

I have selected Rounded Dark as theme. When VS starts the rounded corners look elegant, and upon finishing loading it then applies some white outline?

Initially:

Eventually:

If I switch to another program and return to VS, the original appearance has returned until I resize the panel slightly and then the white outline-like appearance returns.

[VectorStyler]

@Ingolf I will try to replicate this issue.