We have a large zip file (25GB) containing mosty pdfs and png files. (about 150000 files)

When we unzip the file using windows explore some of the content is corrupted. Some png files shows content of other png files, some pdf's won't open. Some are ok. 

When we unzip the file using 7zip everything is ok. The zip file was packed on a 2008 server sent over ftp and unpacked on a 2008 server. 

Have anybody seen anything like this before and can explain why the explore unpack corrupts the files? 

It's very concerning that explore doesn't crash or show an error message if it fails.