Problem chain loading Jessie's pxelinux via http using iPXE (failed to load ldlinux.c32)

[Gary Richards <gary_debian@dsnine.co.uk>]

Hi,

I have an iPXE setup that allows me to chain load the Debian installer
pxelinux setups over http so I don't need to mirror all the things
locally, but so I still get the nice installer boot menu

The iPXE config is essentially this:
set 209:string cfg/pxelinux.cfg
set 210:string
http://ftp.nl.debian.org/debian/dists/${debian_version}/main/installer-${debian_arch}/current/images/netboot/
chain ${210:string}pxelinux.0

Until Jessie it's worked fine for years. pxelinux.0 is downloaded and
having already set the two dhcp options above, it happily manages to go
and find the pxelinux.cfg/default file and then all of the other things
required by it and I get the installer boot menu.

With Jessie however, it seems to get pxelinux.0 ok, but then fails
miserably at finding ldlinux.c32. It simply tells me Failed to load
ldlinux.c32.

I see the pxelinux.cfg/default file now contains an additional parameter
path debian-installer/amd64/boot-screens/ which is where ldlinux.c32
seems to live. Pxelinux never gets as far as actually downloading that
file to find that information before it tries to download ldlinux.c32.
So I thought perhaps that this new path was confusing something and it
was requesting ldlinux.c32 from the wrong location on the web server.
But with the aid of tcpdump it seems that no http request is even made
for ldlinux.c32. In actual fact, no network request at all seems to be
being made for the file.

I'm pretty stuck and have no idea how I might go about getting this
working for Jessie, so I wonder if anyone has any ideas that might help
me?

Thanks

Gary