When I wrote PHP, I never felt comfortable with associative arrays and sequential arrays being almost indistinguishable. Part of that is my Perl heritage, I'm sure, but the slight cognitive load it reduced in choosing your data structure always seemed vastly dwarfed by the extra complexity of umpteen different functions that work on arrays in different ways and the confusion it can cause when you didn't receive exactly what you were expecting and ended up with non-numerical keys when you expected numerical ones or vice-versa (as in this case).

I guess it's just another example of the Waterbed Theory[1].

1: http://en.wikipedia.org/wiki/Waterbed_theory