Comment 3 for bug 192330

As explained in "man unzip":
"Multi-part archives are not yet supported, except in conjunction with zip. (All parts must be concatenated together in order, and then "zip -F" must be performed on the concatenated archive in order to "fix" it.) This will definitely be corrected in the next major release."

This should be fixed however, until the 'real' multi-part support arrives with the 6.0 release

Note: Ubuntu could use the betas for 6.0 in the devel releases, providing extra bug triaging.