I have the same problem, but slightly different conditions.
Core/hybrid is an old Pentium4, MD is an ASRock 330 with Atom 330 dual core.
In the web interface I can find the MD as device 38 and all looks OK, architecture is set to i386, same for the Core. But when doing a net boot it comes down to the "Running Diskless_Setup.sh" or "We announced ourselves..." part and then hangs. Just before the architecture is noted as AMD64. When updating the web interface, the architecture for the MD is still i386.
I'm running with a Realtek RTL-8139/8139C/8139C+ (rev 10) driver
Any thoughts on this?