"Re:" subject mail issue

[Vangelis forthnet]

 Hello.

Can someone please explain why this post by James Cook at 

http://www.mail-archive.com/get_iplayer@lists.infradead.org/msg04353.html

is visible in the secondary mail archive (www.mail-archive.com)

while it is invisible in the main archive (lists.infradead.org) here:

http://lists.infradead.org/pipermail/get_iplayer/2013-July/date.html

(only the sender's name is shown, which is not clickable...)

 I only use the infradead archive to read and post, since this way the 
threading is maintained...

TIA, 
V.