Is there any chance you could explain in a couple words how you concluded that this is a Unity bug? Cheers!
I spoke with a Unity engineer directly who confirmed this had been a known issue for years. They actually fixed it in 2019.3 (or maybe slightly before, I can't remember), but due to the complexity of the fix they refused to backport it to 2018.4. If you upgrade your Unity install you should notice that the edit collider buttons actually work in Peek now.
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