I got curious about this and downloaded this ePub with MathML in it:
https://github.com/IDPF/epub3-sample...r-algebra.epub
It converts to KFX successfully and looks fine when I side load and view it on Scribe (there is some weird formatting that interferes with active canvas but the writing toolbar displays).
Then I converted the KFX to ePub: no more MathML, it is all replaced with inline SVG!
The same ePub, sent to Send To Kindle, downloads as AZW3 on Scribe and Kindle for PC (the version I have 'pinned', not the current one). It appears iPadOS/macOS/Android get KFX (Justification option, page flip). Since this is DRM free maybe I can get the KFX to look at ?(didn't think of that).
The AZW3's in this case are garbage, the mathML expressions are gone and only what text was in there is left. But the KFX is fine. So there is some issue with S2K and MathML when it tries to convert to AZW3.
...
This appears to mirror the behavior of the sample for the
Restarting The Future book: AZW3 on Kindle and Kindle for PC, KFX in the other Kindle apps. I assume the whole book in AZW3 does not have issues rendering MathML but the sample didn't have any such expressions. But maybe there are issues (as in my test), but they are not obvious because book does not have many MathML expressions in there?
BTW @jhowell how did you determine it had MathML?
At any rate it is puzzling why they cannot just deliver KFX everywhere since converting MathML to SVG works.
(Some months ago I became very unhappy for some reason with one of my math books, which started life in Topaz format, and after converting to ePub -- and fixing MANY typos because Topaz is not WYSIWYG -- I set about converting SVG objects to MathML as 'an exercise.' I got about half way before other things shelved the project. I probably won't get back to it, but found it instructive and even fun.)