Dear Michael,
Some recent work on NDPI pyramid generation for our upcoming 5.1 release should have addressed this issue, but 5.0.8 does not contain this work. If you wanted to test this for yourself with a prerelease build, it's available here:
http://downloads.openmicroscopy.org/omero/5.1.0-m4/ (-m5 should be available soon)
Alternatively, if you would like us to take a look to confirm this, if you could upload an example file (or zip of the files) here:
http://qa.openmicroscopy.org.uk/qa/upload/then we can test an import of it into our test server and check it there.
Kind regards,
Roger