First, thanks for the clarification.

However, as far as I can tell, what you are saying comes down to:

Two hashes containing identical keys and values, will iterate in different orders, unless they were constructed in exactly the same way.

For example:

$h1{ $_ } = 1 for         'a'..'z';;
$h2{ $_ } = 1 for reverse 'a'..'z';;

print %h1; print %h2;;

w 1 r 1 a 1 x 1 d 1 j 1 y 1 u 1 k 1 h 1 g 1 f 1 t 1 i 1 e 1 n 1 v 1 m 
+1 s 1 l 1 c 1 p 1 q 1 b 1 z 1 o 1
w 1 a 1 r 1 d 1 x 1 j 1 y 1 u 1 h 1 k 1 g 1 f 1 i 1 t 1 e 1 n 1 v 1 m 
+1 s 1 l 1 c 1 p 1 b 1 q 1 z 1 o 1
[download]

And:

@h1{ 'a'..'z', 'A'..'Z' } = (1)x52;;
delete @h1{ 'A'..'Z' };;

@h2{ 'a'..'z' } = (1)x26;;

print %h1; print %h2;;
a 1 d 1 j 1 y 1 u 1 k 1 g 1 t 1 e 1 v 1 s 1 c 1 q 1 b 1 z 1 w 1 r 1 x 
+1 h 1 f 1 i 1 n 1 m 1 l 1 p 1 o 1
w 1 r 1 a 1 x 1 d 1 j 1 y 1 u 1 k 1 h 1 g 1 f 1 t 1 i 1 e 1 n 1 v 1 m 
+1 s 1 l 1 c 1 p 1 q 1 b 1 z 1 o 1
[download]

And:

@h{ 'a'..'z', 'A'..'Z' } = (1)x52;;
delete @h{ 'A'..'Z' };;

%h2 = %h;;

print %h; print %h2;;
a 1 d 1 j 1 y 1 u 1 k 1 g 1 t 1 e 1 v 1 s 1 c 1 q 1 b 1 z 1 w 1 r 1 x 
+1 h 1 f 1 i 1 n 1 m 1 l 1 p 1 o 1
w 1 r 1 a 1 x 1 d 1 j 1 y 1 u 1 h 1 k 1 g 1 f 1 i 1 t 1 e 1 n 1 m 1 v 
+1 s 1 l 1 p 1 c 1 q 1 b 1 z 1 o 1
[download]

In all cases above, two "identical" hashes were arrived at through a different sequence of operations; and that difference in the sequence of construction manifests itself in a different iteration sequence.

But that has always been the case!

The above is 5.10; but the same is also true going right back to my involvement with perl: 5.6.1.

Which makes me wonder whether your meditation isn't a little a) redundant; b) slightly scare mongery?

Please don't take that the wrong way; I'm simply trying to understand exactly what difference(s) the latest changes have actually made?