Please note that since 5.20 this alone is no nonsense anymore.

Though applying Keys on it is not allowed/making sense.

See my last post

> keys( %$_ ) [0] Nonsense

This is not what happens, but

keys ( %{$_}[0] )

Update

Demo in debugger

$perl -db0
...
  DB<4> $_ = [ qw/a b c d/ ]

  DB<5> x %$_[0,2,1]
0  0
1  'a'
2  2
3  'c'
4  1
5  'b'
  DB<6> say %$_[0,2,1]
0a2c1b
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