Investigate under arrows about unicode-math HOT 3 CLOSED

Test case from amsmath-testmath:

% !TEX TS-program = xelatex 
% !TEX encoding = UTF-8
\documentclass{minimal}

\usepackage{amsmath}
\usepackage{unicode-math}
\setmathfont{Cambria Math}

\begin{document}
\begin{align*}
    \overrightarrow{\psi_\delta(t) E_t h}&
    =\underrightarrow{\psi_\delta(t) E_t h}\\
    \overleftarrow{\psi_\delta(t) E_t h}&
    =\underleftarrow{\psi_\delta(t) E_t h}\\
    \overleftrightarrow{\psi_\delta(t) E_t h}&
    =\underleftrightarrow{\psi_\delta(t) E_t h}
\end{align*}
\end{document}

The \over***arrows are not extended, and \underrightarrow & \underleftarrow are invisible. Only \underleftrightarrow is correctly sized & positioned, and it is made up of \relbar parts. (The PDF display in TeXworks has a bug that makes this sort of thing visible.)

Changing the font to Asana Math, \overrightarrow, \overleftarrow, & underleftrightarrow are correct; \overleftrightarrow is not extended; and \underleftarrow & \underrightarrow are drawn overlapping the cross-bar of the ‘t’.

With XITS Math, \overleftrightarrow is not extended; \overrightarrow & \overleftarrow have their heads centered over the {…}; and \underleftarrow & \underrightarrow are again drawn at cross-bar height—but they are all single glyphs. Only (the correctly-positioned) underleftrightarrow is made of \relbar parts.

STIXGeneral expands only underleftrightarrow (with \relbar), and positions all but \underleftarrow & \underrightarrow correctly; those are again drawn a bit above mid-line.

I tried a test file on all of these fonts with Windows Notepad:
U+20D7 ◌⃗ U+20EF ◌⃯
U+20D6 ◌⃖ U+20EE ◌⃮
U+20E1 ◌⃡ U+034D ◌͍
Whether the font implements these characters does not seem to bear on how the TeX constructions display.

This is very odd.

from unicode-math.

In LuaTeX, under and over arrows should use \Uunderdelimiter and \Uoverdelimiter like ConTeXt.

from unicode-math.

Fixed using over and under accents with both engines.

from unicode-math.