I'm sorry but that is not the cause. That feature has no influence on plugins/downloads at all.
I guess this has been caused by some buggy video information within the stream itself. Or some error in plugin, downloading different video than expected.
I've downloaded the file 10 times. each time it was correct length.
I suggest to enable log debug, Settings-Advanced Settings, search for debug and enable log debug. Restart JDownloader. When it happens again, please close your JDownloader and zip your logs folder and send to
support@jdownloader.org
Then we can check it.