pdf attachment with content-type octet-stream fails to show in Thunderbird

Using:

• Provider: dev.bitmask.net
• Bundle: Bitmask-linux64-2014-01-18-12e7ae35

Steps to reproduce:

• Configure your account in thunderbird.
• Send an email from Thunderbird containing a 5 MB attachment.
• Wait for email to arrive.
• Try to see the attachment.

What happens to me is:

• The little clip icon in TB message list shows that the message contains an attachment.
• When I click on the message, the clip icon disappears and I can't find any attachment in the message.
• If i save the message to disk an inspect it, i see that there the bit attachment is there.

(from redmine: created on 2014-01-20, closed on 2015-09-10, relates #6773 (closed))