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henkvdb - the question is why did the uninstall not delete the install directory - map
The usual reason is because some component of the application is in use (running). Maybe calibre.exe, ebook-edit, ebook-viewer or a calibre command line program, calibre-server is another possibility. If a component is in use then the uninstaller usually won't remove it or the directory. And I have seen stranded calibre-parallel processes, but not for a while and I can't recall the circumstances.
BR