The "file" cannot be moved (deleted) on Windows, but it can be moved on linux. Why?

WindowsFileHandling.java

Logger logger = LoggerFactory.getLogger();
FTPClient ftpClient = new FTPClient(); // from commons-net

public void upload(File file) {
    InputStream is = null;

    try {
        is = new BufferedInputStream(new FileInputStream(file));
        this.logger.debug("Uploading file");

        if (this.ftpClient.storeFile(file.getName(), is)) {
            this.moveToSentDirectory(file);
        }
        else {
            this.logger.error("Failure uploading file");
        }
    }
    catch (Exception e) {
        this.logger.error("Failure uploading file", e);
    }
    finally {
        Closeables.close(is);    // closes silently, but logs errors
    }
}

private boolean moveToSentDirectory(File from) {
    File to = new File(this.workDirectory + File.separatorChar + this.sentDirectory + File.separatorChar + from.getName());

    try {
        this.logger.debug("Moving file [from={},to={}]", from, to);
        Files.createParentDirs(to);
        Files.move(from, to);    // this throws an IOException
        return true;
    }
    catch (IOException ioe) {
        this.logger.error("Failure moving file [from=" + from + ",to=" + to + "]", ioe);
    }
    return false;
}