doxygen incorrectly handles parameter names with umlauts in C#

[reini]

Binary package hint: doxygen

I am trying to document a constructor:

        /// <summary>
        /// Initialisiert diesen IdErzeuger mit einem Präfix ohne Zähler.
        /// </summary>
        /// <param name="präfix">Der Präfix.</param>
        public IdErzeuger(string präfix)
            : this(präfix, false)
        {
        }

Which results in the following warnings:
IdErzeuger.cs:33: warning: argument 'pr' of command @param is not found in the argument list of Iev.IdErzeuger::IdErzeuger(string präfix)
IdErzeuger.cs:33: warning: argument 'auml' of command @param is not found in the argument list of Iev.IdErzeuger::IdErzeuger(string präfix)
IdErzeuger.cs:33: warning: argument 'fix' of command @param is not found in the argument list of Iev.IdErzeuger::IdErzeuger(string präfix)
IdErzeuger.cs:33: warning: The following parameters of Iev::IdErzeuger::IdErzeuger(string präfix) are not documented:
  parameter 'präfix'

When I open the compiled HTML and man documentation, the parameter is documented correctly.

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: doxygen 1.7.1-1
ProcVersionSignature: Ubuntu 2.6.35-24.42-generic 2.6.35.8
Uname: Linux 2.6.35-24-generic x86_64
Architecture: amd64
Date: Mon Dec 27 01:45:16 2010
InstallationMedia: Kubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101008)
ProcEnviron:
 LANGUAGE=
 PATH=(custom, user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: doxygen

[paolog (paolo-greppi)]

Unreproducible with doxygen 1.9.1 on Debian 11 (bullseye). I saved the C# snippet above as a.cs with cp1252 encoding, set INPUT = a.cs and updated Doxyfile with doxygen -u.
No warning is issued.
I attach the full example.