QT_EXCLUDE_SOURCES_FROM_TRANSLATION not working as expected

I have a cmake project which uses several 3rd-party libraries (e.g. the Boost-library) to build. Furthermore it uses translations via the qt_add_translation command. But since QT 6.7.1 the extraction of the strings with the lupdate-tool takes an awful lot of time. What was usually a matter of seconds, now takes several hours !
I found and used the new property QT_EXCLUDE_SOURCES_FROM_TRANSLATION, which was introduced in Qt 6.7 but to no avail.

I used the following command sequence in cmake:
(with ${Boost_INCLUDE_DIR} = "/usr/include")

set_property(TARGET rde PROPERTY QT_EXCLUDE_SOURCES_FROM_TRANSLATION ${Boost_INCLUDE_DIR})
qt_add_translations(rde
    TS_FILES assets/i18n/en.ts assets/i18n/de.ts assets/i18n/fr.ts
    SOURCE_TARGETS rde
    LUPDATE_OPTIONS -locations none
)

These cmake commands result in the following lupdate_project.json file:
(The file is stripped by several paths and filenames for reasons of clarity!)

{
  "projectFile": "<MyPath>/CMakeLists.txt",
  "includePaths": [  ],
  "sources": [  ],
  "translations": [ "<MyPath>/assets/i18n/en.ts", "<MyPath>/assets/i18n/de.ts", "<MyPath>/assets/i18n/fr.ts" ],
  "subProjects": [
    {
      "projectFile": "<MyPath>/CMakeLists.txt",
      "includePaths": [ "<MyPath>/build/Desktop_Qt_6_7_1-Debug/rde_autogen/include", "<MyPath>/RDS/Rds/", ... <snip> ... "/usr/include", ... <snip> ... "/usr/include", ... <snip> ],
      "sources": [ "<MyPath>/build/Desktop_Qt_6_7_1-Debug/rde_autogen/mocs_compilation.cpp", "<MyPath>/src/main.cpp", "<MyPath>/src/mainwindow.h", "<MyPath>/src/mainwindow.cpp", ... <snip> ...  ],
      "excluded": [ "/usr/include" ]
          }
  ]
}

As you can see, the "/usr/include" path (= ${Boost_INCLUDE_DIR}) lands in the "excluded"-line correctly, but also (several times !) in the "includePaths"-line, where it forces lupdate to take a loooong time to finish (here > 6 hours !).

After removing all occurences of "/usr/include" manually from the "includePaths"-line of the  lupdate_project.json file before re-running lupdate (from the command -line), lupdate returns successfully almost instantly !

• Why the property QT_EXCLUDE_SOURCES_FROM_TRANSLATION doesn't work to remove all occurences of "/usr/include" from the includePaths-line of the lupdate_project.json file ?
• Why does lupdate take sooo much time to process the (here: Boost-) library ?