Strange hinting of precomposed character

[Brad Neimann]

I’ve attached an interesting hinting problem seen ‘in the wild’. The 
image shows text ⟨ɑ̃ ɛ̃ ẽ ø̃⟩, rendered with  Firefox 116.0b5 in font 
Noto Sans Regular at zoom levels varying from 100% to 210%. (Although I 
can reproduce the problem with ftstring too, as long as I force 
auto-hinting). Note that the precomposed character ⟨ẽ⟩ exhibits far 
worse hinting than the combining diacritics around it. What’s more, as I 
zoom in, the precomposed tilde flips back and forth between rendering as 
a horizontal bar and as a tilde — and at the highest zoom level it looks 
distinctly different to the combining tilde. Can anyone explain what’s 
happening here? I would expect that, if the diacritic is to be hinted as 
a horizontal bar, that would occur only at the smallest sizes, and would 
equally affect the combining diacritic too.

Regards,
Brad