https://drafts.csswg.org/css-flexbox/#min-size-auto

Nonetheless, although this may require an additional layout pass to re-resolve percentages in some cases, this value (like the min-content, max-content, and fit-content values defined in [CSS-SIZING-3]) does not prevent the resolution of percentage sizes within the item.

That should just say something like "This value does not prevent the block-size from being definite when it otherwise would be"

@fantasai @tabatkins