If a mysql is already running during installation of TYPO3Winstaller 4.2.3, and that mysql can not be shut down, then the TYPO3Winstaller installation continues nonetheless, which results in a defunct installation. The setup I had was this:
1) As administrator, I had a TYPO3Winstaller running.
2) I switched to a non-administrator user.
3) I started the installation of TYPO3Winstaller as the non-administrator user.
4) During install, TYPO3Winstaller could not shutdown the already running mysql. That lead to the defunct installation.
TYPO3Winstaller will pop-up a warning from typo3start.log, so this is not critical since the user will know something is wrong.
This feature request is posted in the hopes that an even more elegant solution can be implemented.