When setting a label's showBackground to true, other labels will have a black outline.

[appleshowc]

What happened?

None of the labels have an outline set.
When I set one of the label's showBackground to true, other labels will have a black outline.
I think that the other labels shouldn't be affected. The other labels should remain as they are, with no outline at all!

Reproduction steps

1.Setting a label's showBackground to true, other labels will have a black outline.

2.All labels have set showBackground to false, other labels will NOT have a black outline.

Sandcastle example

https://sandcastle.cesium.com/index.html#c=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

Environment

Browser: Chrome 131.0.6778.140
CesiumJS Version: 1.124
Operating System: Windows10