Apple Mail: Attachments 'paper clip' icon is missing from Sent Mail (Mavericks)

I often need to sort Sent mail for messages containing attachments. Since I upgraded to Mavericks, the paper clip (Attachments) icon is missing from new (post-Mavericks upgrade) messages listed in the Sent Mail folder.

I've rebuilt and reindexed my mailboxes several times, turned the Attachments column view on and off, but still no luck.

Has anyone else had this problem? Without being able to quickly and accurately find which sent messages have attachements, I'll have to quit Mail for good.

-- CM