themes Tsubaki: changing 'all' Heading font in Styles does nothing

Edit: Please see https://github.com/Automattic/themes/issues/7152 for larger context and workarounds (also noted below)

Quick summary

If you use the Styles menu within the Site Editor, and try to change the font family for all headings at the same time, nothing happens.

Steps to reproduce

open a site using the Tsubaki theme
add some heading blocks that you can see in the Site Editor
in the Site Editor, open Styles > Typography > headings
leave the "All" option selected (rather than choosing H1 or H2 etc individually) and change the font to any of the available options:

note: changing the font for H1 or H2 etc individually works, but if you try to select default from the dropdown (which I assume would make them use the font set under all, it immediately reverts to system font instead

What you expected to happen

The fonts for all Heading elements should be changed, unless they're overridden at the individual level

What actually happened

no font change occurs

Context

reported in 39140532 and followed up in 5824343-zen

Platform (Simple, Atomic, or both?)

Atomic

Theme-specific issue?

Tsubaki

Browser, operating system and other notes

No response

Reproducibility

Consistent

Severity

Some (< 50%)

Available workarounds?

Yes, easy to implement

Workaround details

Users can still set the font family for Headings by setting them at each level individually. Setting h1, h2, h3, h4, h5 and h6 each to the same font has the same effect as changing all fonts at once, but is more labor-intensive