DB<82> $hash{$_} = $value  for @keys;

  DB<83> x \%hash
0  HASH(0x3598330)
   'Prefix1=A:b:1' => HASH(0x35a48e8)
      'a' => 1
      'b' => 2
   'Prefix1=A:b:2' => HASH(0x35a48e8)
      -> REUSED_ADDRESS
   'Prefix1=A:c:1' => HASH(0x35a48e8)
      -> REUSED_ADDRESS
   'Prefix1=A:c:2' => HASH(0x35a48e8)
      -> REUSED_ADDRESS
  DB<84> p $hash{'Prefix1=A:b:1'}{a}
1
  DB<85> p $hash{'Prefix1=A:b:1'}{b}
2
  DB<86> p $hash{'Prefix1=A:c:2'}{b}    # reading works!
2
  DB<87>