Thanks for reporting @starball and sorry for the bug! I'm happy to report that this bug is fixed as of an update pushed out yesterday.
This issue arose because styles on our button component's filled variant (.s-btn__filled) were being superseded by rules applied on :not(.s-btn__outlined). The filled and outlined variants are usintended to be used exclusively from one another, so we increased specificity by applying filled styles to elements that matched .s-btn__filled:not(.s-btn__outlined) to resolve this issue.
For more context and details, check out the pull request for this fix in our design system. To see the specific code change made to resolve the problem, see the changes made to button.less.