Why can I collect a parallel stream to an arbitrarily large array but not a sequential stream?

Question

From answering this question, I ran into a peculiar feature. The following code works as I assumed it would (the first two values within the existing array would be overridden)

Answer 1

The generator function is required to produce "a new array of the desired type and the provided length." If you don't comply with the spec, behavior is undefined.