newpxmath: accents are always bold

Question

When using newpxmath, the accents in math mode are always bold, regardless of whether the letter underneath is bold or not:
documentclass{article}
  
usepackage[T1]{fontenc}
usepackage{newpxtext}
usepackage{newpxmath}

begin{document}

centering

$hat{a}$ $tilde{a}$ $bar{a}$ $check{a}$ $dot{a}$ $acute{a}$ $grave{a}$ $breve{a}$

^a ~a =a v a .a 'a `a u a

textbf{^a ~a =a v a .a 'a `a u a}

end{document}

In the image above, the first line is math mode (medium), the second line is text mode (medium) and the third line is text mode (bold). It can be clearly seen that the accents in math mode are bold.
Is this a bug in newpxmath or am I missing something?

Edit: It seems that the symbol font npxsy is corrupt. If you create a font table with
documentclass{article}
  
usepackage[T1]{fontenc}
usepackage{newpxtext}
usepackage[scaled=1.042]{zlmtt}
usepackage{newpxmath}
usepackage{fonttable}

begin{document}

xfonttable{LMS}{npxsy}{m}{n}

pagebreak

xfonttable{LMS}{npxsy}{b}{n}

end{document}

you can see that the accents in slots 158–168 look the same in medium and bold weight. The other characters, however, have different medium and bold variants (as it should be).
(There is another unrelated bug: the symbol in slot 11 is mirrored in bold.)

Update: This issue has been fixed since newpx version 1.423.

egreg · Accepted Answer

Update 2021-06-02
Version 1.423 (released 2021-05-31) of NewPX fixes the issue. From the README file

Changes in version 1.423

Corrected weight of regular math accents, which were rendering in bold weight.
Corrected the bold symbol circledivide in bold weight. (It was inexplicably mirrored.)

The OP's example now produces

(I've only added a couple of missing accents.)
Original answer
The characters are taken from the font pxsys (via a virtual font). Some time between 2019 and 2020, probably due to an error in assembling the fonts, the accents in pxsys have become boldface.
While you wait for a fix, you can redefine the accents to use the operators font (which newpx tries to avoid for good reasons, but we're in an emergency here).
documentclass{article}
  
usepackage[T1]{fontenc}
usepackage{newpxtext}
usepackage{newpxmath}
usepackage{amsmath}

makeatletter
re@DeclareMathAccent{grave}{mathalpha}{operators}{"12}
re@DeclareMathAccent{acute}{mathalpha}{operators}{"13}
re@DeclareMathAccent{check}{mathalpha}{operators}{"14}
re@DeclareMathAccent{breve}{mathalpha}{operators}{"15}
re@DeclareMathAccent{bar}{mathalpha}{operators}{"16}
re@DeclareMathAccent{mathring}{mathalpha}{operators}{"17}
re@DeclareMathAccent{hat}{mathalpha}{operators}{"5E}
re@DeclareMathAccent{dot}{mathalpha}{operators}{"5F}
re@DeclareMathAccent{tilde}{mathalpha}{operators}{"7E}
re@DeclareMathAccent{ddot}{mathalpha}{operators}{"7F}
makeatother

begin{document}

centering

$hat{a}$ $tilde{a}$ $bar{a}$ $check{a}$ $dot{a}$ $acute{a}$
$grave{a}$ $breve{a}$ $ddot{a}$ $mathring{a}$

^a ~a =a v a .a 'a `a u a "a r a

textbf{^a ~a =a v a .a 'a `a u a "a r a}

end{document}

newpxmath: accents are always bold

One Answer

Update 2021-06-02

Original answer

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