Different image permissions and name prefixes with \Zend\Filter\File\RenameUpload

Hi, guys!
I am using \Zend\Filter\File\RenameUpload::class as apigility filter. I get uploaded images with different permissions and name prefixes.

$ ls -la
-rw-r--r-- 1 www-data      www-data      134730 Feb 12 14:11 phprb5a4q_5e43eb71a320a0_86088736.jpg
drwxrwxrwx 2 someuser      someuser        4096 Feb 12 14:11 small
-rw------- 1 www-data      www-data      148241 Feb 12 13:50 zfcjjvwRD_5e43e6920ced84_73754641.jpg
-rw------- 1 www-data      www-data      256846 Feb 12 13:49 zfcVmMlTT_5e43e65d272426_70899995.jpg
-rw------- 1 www-data      www-data       60530 Feb 12 14:09 zfcxcxbkE_5e43eadc9e64e7_97584177.jpg

As you can see some filenames has “php” prefix and have normal permission (644) but some images have prefix “zfc” and permission (600).