g1smd - 8:59 pm on Jun 11, 2012 (gmt 0)
If the correct single-step 301 redirect is in place, Google will figure it out.
Partial showing of previews is quite common. Allow a few weeks for Google to pull in all the elements of the page.
For URLs which now redirect, the preview will be the first thing to no longer show up. The snippet is often the next thing to go.
The cache view is not at all the same thing as a preview. There's many reasons why the cache view can be missing.
Make sure the site is tecnically 100% correct. Check all the reports in WMT and act on them and then allow three months for things to fall into place.