A case where slash is incorrectly interpreted as division

[andrew-skybound]

Test Case (Sass 3.4.16):

div {
    foo: (1 (1/2) 2px/3px 2px/3px);
    foo: ((1/2) 2px/3px 2px/3px);
}

Output CSS:

div {
  foo: 1 0.5 2px/3px 2px/3px;
  foo: 0.5 0.66667 2px/3px;
}

Notice that removing the 1 from the start of the list causes the / in the 3rd item to be computed as division instead of left as a delimiter.

Is this behavior expected? The third value doesn't seem to meet any of the criteria for division as explained in the documentation, and even if I misread the documentation and it did meet the criteria, wouldn't the 4th item also be computed as division?