NASM will silently accept 'mov [mem], label' without size specifier.

[krinor]

For example, 'mov [es:bx], label' will assemble to 'mov BYTE [es:bx], label' without any complaints. In other words, only the low byte of the address to 'label' will be used, which is probably not what the programmer intended.

To avoid programmer hair loss, NASM really should complain if someone forgot to add a size specifier. :)

[hpax]

Yes, this is a bug.