iOS Mail wont open zip files I'm on iOS 9.2 on an iPad air 2.

I understand that since iOS 7 mail should open (for viewing) zip files directly.

What I actually get is just perpetual Loading... and spinning wheel. If I copy to WinZip I can open the file fine.

Is this expected behaviour?

....... Further (!) Edited to add the following in response to bmike's comment and add context ......

5 small to moderate PDF files of business documents, total zipped size 364KB.  Zipped using WinZip 18.5 on desktop Win7. Zip file was attached to an email.

Outlook 2013 opens the zip file on double-clicking (showing the zip file index).
Interestingly, Yahoo Mail shows the zip file as "No Preview" (download is Ok).

On iPad, both the 5 documents, and also a test single document, produce a perpetual spinning wheel when the zip file icon is tapped for native view.
Using 'copy to' (touch and hold the icon) with PDF EXpert or to WinZip mobile, either file can be opened successfully.

I will look for a different zip program on the desktop to see if that makes a difference.

...

What has me quite puzzled is that Google has turned nothing on this topic, trying various searches.   Which suggests this is a somewhat unique situation.  (Or no one is using Mail App for serious emails ...)

But to me this is a very straightforward situation.  And given the facts in the question, the finger does seem to point at Mail.app.
After my test (ipad air 2 with 9.3.2) i see that MAIL opens only zip files produced with a MAC OS X.
With MAIL we can't open zip files produced on other operating system /app (for example windows or 7zip on windows, etc)
So their info 
("Supporto allegati email/Tipi di documenti visualizzabili" on https://support.apple.com/kb/SP708?viewlocale=it_IT&amp;locale=it_IT)
are not true (or are partially true)