Email headers in Clearwell Review

We would like to make email headers (same as internet headers in Outlook - Message Properties) available under Clearwell case review. We are not interested in searching headers at this point, just to make them available to our case reviewers.

I have a case with a single PST file, first I checked "Enable email header reviewer" option under "Enable/disable additional case features" section, and processed the case without any errors. This makes "click to view Internet Headers" option available under Analysis & Review. Which is very handy, but when I click the icon, a new window pops open and displays: [This message has no headers.]  In fact, there are 2000+ items in the PST, and only 11 of them displays headers, all the rest are giving me [This message has no headers.] message. I can open the PST file in Outlook and see headers for every email. Is there a trick in Clearwell to make internet headers visible for all PST email items?

Thank you