works like a charm.
I feel pretty stupid now, that'd have been the last place I would have looked. That also fixed an issue with the Connection header being set to "keep-alive, close" since it's possible to set a proper Keep-Alive header like this:

local @LWP::Protocol::http::EXTRA_SOCK_OPTS = (
   SendTE => 0,
   KeepAlive => 1
);
[download]

Thank You!