When items can't be baseline-aligned, they are fallback-aligned. In flexbox, this falls back to flex-start. In the alignment spec, it falls back to start. Both of these seem wrong. It should fall back to self-start (or its equivalent), which is the direction that things appear to align to if you have a mix of content with different amounts of text.

(last-baseline should of course align to self-end).

https://drafts.csswg.org/css-flexbox/#valdef-align-items-baseline
https://drafts.csswg.org/css-align/#valdef-justify-content-baseline