With objdump (2.15.93 20041010) built for i386-pc-mingw32
disassembly to intel syntax outputs 64-bit register names
mxed in with the expected 32-bit names.

For example

/* foo.c */
void foo() {}

gcc -c foo.c
objdump -d -mi386:intel foo.o

gives:

foo.o:     file format pe-i386

Disassembly of section .text:

00000000 <_foo>:
   0:	55                   	push   rbp <<<<<
   1:	89 e5                	mov    ebp,esp
   3:	5d                   	pop    rbp <<<<<
   4:	c3                   	ret    
   5:	90                   	nop
....

objdump to default AT&T syntax works fine.