CSS Align had this sentence, which has been sitting around for awhile:

For the purposes of finding the first (last) baselines of a box, it and all its in-flow descendants with a scrolling mechanism (see the 'overflow' property) must be considered as if scrolled to their origin (final) position.

CSS2.1 had this sentence:

The baseline of an 'inline-block' is the baseline of its last line box in the normal flow, unless it has either no in-flow line boxes or if its 'overflow' property has a computed value other than 'visible', in which case the baseline is the bottom margin edge.

Myles raised an issue against CSS2.1 https://lists.w3.org/Archives/Public/www-style/2015Mar/0342.html requesting a change to make overflow have a less dramatic effect baseline alignment. which the CSSWG later accepted https://lists.w3.org/Archives/Public/www-style/2015Apr/0144.html

I'm reraising this issue because I think the wording in CSS Box Alignment seems to solve Myles' issue in a somewhat more useful way, and perhaps we should reconsider how last-baseline alignment works in the presence of overflow.