TYPO3 Core

The detectChangedFilesInStorage in FAL indexer detects changed files only if their mtime (modification_date) is newer than the modification_date registered in the corresponding sys_file-record.

But a newer mtime is not the only identifiert of a changed file. For example, if a file is replaced with another - but older one - the mtime of the "new" file might be older than the mtime of the previous file. So if a file with "older" mtime is just copied / upload in order to replace an existing one, the re-indexing is not done.

So we do not only have to check for never mtimes here, but for different mtime.