This ticket describes a known issue, which seems to be a bug in pMBP but is a bug in your ZIP-software.
You backup files from the servers file system and you experience that the ZIP file seems to be empty but the ZIP-file has a size other than 0kb.
Probably the reason for this is, that the first folder in the ZIP-file is called ".." and your ZIP-software (eg. Windows Explorer) can not display this folder.
The reason why the first folder is called ".." is, that the patch of the files to store begins with "..".
Please check, if this error still exists with 7zip (http://www.7-zip.org/). If it does, please create a new ticket here.