Wrong behavior of \hphantom{\!}

[UlyssesZh]

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Describe the bug:

x\,\hphantom{\!}x

There should be no spacing between the two xs, but there is.

To Reproduce:

Expected behavior:
Screenshot of the result rendered by pdflatex:

Screenshots:
reproducing link

Environment (please complete the following information):

• KaTeX Version: 0.16.9
• Device: Desktop
• OS: Ubuntu 20.04
• Browser: Brave
• Version: 1.60.125 Chromium: 119.0.6045.199

Additional context: