Serendipity allowed us to find this really easily, thanks to some old
builds lying around...
The following Seabios commit breaks gpxe boot with e1000:
commit a5826b5ad482f44d293387dc7513e5e98802a54e
Author: Kevin O'Connor <address@hidden>
Date: Sat Oct 24 17:57:29 2009 -0400
Add simple cooperative threading scheme to allow parallel hw init.
Enable system for running hardware initialization in parallel.
The yield() call can now round-robin between "threads".
Rework ata controller init to use a thread per controller.
Make sure internal drives are registered in a defined order.
Run keyboard initialization in a thread.
Rework usb init to use a thread per controller.