jit.uldl downloads non existant files

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I am working on network with over 100 Laptops which need to
exchange some data, and I want to use jit.uldl to download
some images, and send confirmation to master via udp that download
succeeded.
But jit.uldl creates false documents for non existant files
and reports download as success, if it allready downloaded anything
from same http source.

If one peeks inside, it is actually html error 404 not found
Max 6.1.10 and 7.3.5 on OSX produce the same mistake.
Has anyone any explanation for that ?
using ftp works as expected, so I can make my way arround,
but it makes me wonder what's wrong if download uses http