Sorry for the constant spamming! It looks like my problem is related to 
PR 26007:
http://www.netbsd.org/cgi-bin/query-pr-single.pl?number=26007

The problem is that CPPFLAGS+= -DEPIA_HACK hasn't been added to 
pxeboot/Makefile. Patch below:

Index: sys/arch/i386/stand/pxeboot/Makefile
===================================================================
RCS file: /cvsroot/src/sys/arch/i386/stand/pxeboot/Makefile,v
retrieving revision 1.11
diff -u -r1.11 Makefile
--- sys/arch/i386/stand/pxeboot/Makefile        25 Jun 2006 14:12:14 -0000 
1.11
+++ sys/arch/i386/stand/pxeboot/Makefile        18 Aug 2006 13:32:48 -0000
@@ -57,6 +57,7 @@
  #CPPFLAGS+= -DNFS_NOSYMLINK

  CPPFLAGS+= -DPASS_MEMMAP
+CPPFLAGS+= -DEPIA_HACK

  #CFLAGS= -O2 -fomit-frame-pointer -fno-defer-pop
  CFLAGS+= -Wall -Wmissing-prototypes -Wstrict-prototypes -Wno-main

-- 
Stephen