The error we're hitting is this one:
// Fix $MFT
// DI - pointer to buffer
// BX - attr cur
orb $NT_FG_GPOS, nt_flag
cmpw nt_attr_end, %bx
(The 1: label is the start of a loop, so see the source file for context if you care.)
I've checked against grub4dos 0.4.4, which seems to be the latest release. There are some differences between its ntfsbs.S and that in grub2/ntldr-img, which it probably wouldn't hurt to reconcile at some point, but none of them seem relevant to this.