Same instruction, two opcode encodings

IA32 instruction “adc al,0x7” has two different opcode encodings.

/Users/peter>ndisasm a
00000000  80D007            adc al,0x7

/Users/peter>cat a.asm
bits 16
adc al,0x7

/Users/peter>ndisasm a
00000000  1407              adc al,0x7