The most recent CSSWG discussion agreed that symmetrical letter-spacing is an improvement, but should additionally be trimmed at line edges to maintain expected edge alignment. Applying such trimming at line-start will fix the rendering of this example, and likewise for the "BBB icons" example in bug 1892432. I have a patch for this which I'll post here. Ideally, we should also trim at line-end, but that has much less risk of being a real-world compat issue (we haven't had any such reports filed, AFAIK). I'll file a followup about that aspect.
Bug 1892262 Comment 8 Edit History
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The most recent [CSSWG discussion](https://github.com/w3c/csswg-drafts/issues/10193#issuecomment-2163247458) agreed that symmetrical letter-spacing is an improvement, but should additionally be trimmed at line edges to maintain expected edge alignment. Applying such trimming at line-start will fix the rendering of this example, and likewise for the "BBB icons" example in bug 1892432. I have a patch for this which I'll post here. Ideally, we should also trim at line-end, but that has much less risk of being a real-world compat issue (we haven't had any such reports filed, AFAIK). I'll file a followup about that aspect.