Substitution, subgroups and numbers

Hello, I'm trying to make a perl substitution using Util.substitute and
Perl5Substitution.

The equivalent perl code is:

**********
use strict;
my $v = "foo1";
$v =~ s/([a-zA-Z]+)(\d+)/${1}2/;
print $v."\n";
**********

which outputs:
>foo2

Using Util.substitute the resulting value is:
>${1}2

Then I tried

$v =~ /([a-bA-Z]+)(\d+)/$1\\2/;

which does not work in perl but works with ORO 2.0.6 (mostly due to
different escaping rules when escaping the rightmost part in ORO).

(Anyway I achieve valid substitutions in other cases, which makes me
think that my code is not the real problem).

I am no perl-expert so maybe this kind of groupid escaping is part of
perl 5.6 regexp. In this case, is there an other way to disambiguate the
right part of the substitution ?

Is this a known limitation/bug/feature to come ?
Thanks for any hint.

Trick

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