Why compressed xps are corrupt?

Question

compressed xps documents do not pass isxps.exe test and do not display in xpsviewer. i'm using Windows 7 and vs2010.

Dim ms = New MemoryStream()
Dim P As Package = Package.Open(ms, FileMode.Create, FileAccess.ReadWrite)
Dim DocumentUri As Uri = New Uri("pack://document.xps")
PackageStore.AddPackage(DocumentUri, P)

Dim document As XpsDocument = New XpsDocument(P, CompressionOption.Maximum, DocumentUri.AbsoluteUri)

If i change CompressionOption.Maximum to CompressionOption.None all works perfectly.

IsXps.exe says "Unable to open Zip archive Error code: 0x8000FFFF", same with default W7 XpsViewer.

what i'm doing wrong?

(i've also installed latest 7zip program, but i do not think that it may corrupt the default windows zip capability......or not?)