TYPO3 Core

To reproduce this:

Upload a file called Müller.jpg via

$file = $folder->getStorage()->addUploadedFile($fileUpload->getFileUploadArray(), $folder, NULL, $conflictMode);

Then again upload a file called Müller.jpg. Normally FAL should create a file called Müller_01.jpg (Mueller_01.jpg).
Erroneously the original file will be overwritten.

The problem is, that FAL checks if Müller.jpg exits, but this file does not exist because it will be renamed in Mueller.jpg after upload.
So FAL uploads the new file, renames it in Mueller.jpg and the original file is overwritten.