[Bug-wget] Truncated files ... --ignore-length bug ??

[R.]

Hello

I'm trying to wget a collection of (big) mp4 files.
I have every file URL available, say "http://www.site.com/path/video";.
The site uses a session cookie for authentication.
I have managed to dump this cookie to a local file and use this file 
when connecting to the server for the download process.

I'm using this command line:
wget --load-cookies cookies.txt http://www.site.com/path/somewhere/video

The download seems to proceed fine but eventually I get less than half 
the video ..
Tried many other videos with same results.

With firefox, using page information, I can see the media named "video" 
which is mp4 file. If I click save as firefox will download the whole 
file without a problem.

I tried curl instead of wget: same bad result.

So I tried many options from wget's man page, like --ignore-length and 
others, to no avail.

wget --ignore-length -S output is:
  HTTP/1.1 200 OK
  Date: Tue, 11 Aug 2015 19:57:59 GMT
  Server: Apache
  Vary: Host
  Expires: Sun, 19 Nov 1978 05:00:00 GMT
  Last-Modified: Tue, 11 Aug 2015 19:57:59 GMT
  Cache-Control: store, no-cache, must-revalidate
  Cache-Control: post-check=0, pre-check=0
  P3P: CP="NOI ADM DEV COM NAV OUR STP"
  X-Debug-Data: 21450
  X-Content-Duration: 502.109
  Content-Location: patch/video
  X-Bandwidth-Control: On
  X-Video-Bitrate: 28064.4
  Accept-Ranges: bytes
  Content-Length: 2925253
  Connection: close
  Content-Type: video/mp4
  Longueur: ignoré [video/mp4]

If I do wget -S without --ignore-length the last line becomes "Longueur: 
2925253 (2,8M) [video/mp4]" which is the exact length of the truncated 
file wget manages to download !!

Is wget ignoring my "--ignore-length" flag ??

Sorry for this long message and my poor english level .. I'm french and 
totally confused by this problem ..

Thanks for your help.