Question about Outlook Express

Hi.

I've just noticed an odd behaviour with Outlook 2011 for Mac.  I search for a word/sender/phrase etc.  in a set of mails in a folder.  The search only finds items created on or before 29 November.  For messages after this date the search result is blank - even if I cut and paste a word from the mail into the search box.  The search result is blank or only includes messages prior to 30Nov2012.

Just to be clear - if *** Email address is removed for privacy *** sent me a message about Doom on 28 Nov 2012 and a message about Doom on 6 Dec 2012 and they are still in my Inbox then a search for "xyzzy" or "dungeon" or "*** Email address is removed for privacy ***" or "Doom" will only return the 28 Nov message in the search results.

Spotlight finds all the messages OK  - and the Microsoft data folders are not in the Spotlight  Privacy box, so I don't think it's a Spotlight issue. There are no folders in the Spotlight Privacy box.

I've tried re-building the database with <option+click><rebuild>.  The rebuild reported a successful rebuild but the search behaviour is still as above.

MBA 10.7.5
Outlook 2011 14.2.5

Thanks in advance for any help.