Attach button does not appear on 'reply' comments

Hi,

when I click 'Comment' on a post, I receive the full attachment form including the Attach button and everything works fine.

However, when I click "Reply" I do not see the Attach button. I can still browse to select a file and upload it, but after clicking 'Post Comment' I do not see the attachment under the new replied comment. The upload was successful, though.

Refreshing the page shows the attachment fine, so it seems to be a highly localized UI sort of thing.

I'm seeing this behavior on 5.6 using both the customer's theme and garland, in both FF and Safari.