I've added the requested information to the previous reply. However, to be thorough, I've run the full script on v5.8.0 as well. When using our $x = qr/(??{ $x })/;, the script works as desired. However, when using my $x = qr/(??{ $x })/;, the script throws no strictures errors, but does throw a warning:

$ perl rec_regex.pl
Use of uninitialized value in substitution iterator at perm.pl line 17
+, <DATA> line 1.
<7> { ... } </7>
<7> { { } } </7>
{ <7> { { } } </7> }
{ <3> { } </3> { <7> { { } } </7> } }
<7> { ... } </7>
[download]

Additionally, as you can see it only does the second level of recursion again. Nevertheless, I never used my originally, so just sharing for addition data.

Also note, I just discovered that the original code DOES work currently if declared with our. It just won't pass strictures validation. Will update my original question with this data soon as I get back from pharmacy. Got a toothache coming on.

However, when using my $x = qr/(??{ $x })/;, the script throws no strictures errors

That's the bug I mentioned earlier. The use strict; didn't propagate into the (??{ }). (You're getting the warning because the second $x is the package variable.)

I'm guessing the behaviour of our $x = qr/(??{ $x })/; changed when they fixed the pragma propagation.

I'll file a bug report.