hash weirdness

gistfile1.txt

h = Hash.new([])


h[:a] << 1
h[:a] << 2

h
#=> {}     # WTF
h.keys    
#=> []     # WTF
h[:a]
#=> [1, 2] # OK

h[:b] = 3

h
#=> {:b=>3}  # where is a?
h.keys    
#=> [:b]     # where is a?
h[:b]
#=> 3 # OK
h[:a]
#=> [1, 2] # OK