I suspect it is because the parser expects different things at the different times. Look at the first one for example, it is pretty reasonable for this to be a 3-element array, we often make such assignments. In fact, for us to be able to make such assignments, this has to be a three element array.

In the second case the parser is looking for a subscript instead of another array, so it tries to make what it finds into one.

HTH, --traveler