A Possible "Bug"?

Hi, all,

I've just read and modified some webpages that are
out-of-date due to some reasons. 

For instance, I've deleted some sentences on
http://mlton.org/SMLNJDeviations

related to these code:
val [x] = [[]];
val _ = {1::x, "one"::x}

for that I've tried it in the latest smlnj-110.71, and
it seems that it runs smoothly.

However, I happened to run this code:
val [[x]] = [];

MLton reports a warning message, but smlnj-110.71 reports
an error (compiler bug?). I'd like to ask here that which 
behaves correctly?

Thanks in advance.

-Paul