G'day AnomalousMonk,

"Note that details of this behavior changed somewhere between versions 5.8 and 5.30.)"

I suspect that's 5.26.0: "perl5260delta: scalar(%hash) return signature changed". I don't have a pre-5.26 version handy to test that.

However, there's other things probably going on prior to the code shown in the OP:

• Why is there a newline appended to the hashref? I'd guess there's some sort of suspect code near where that happens.
• Lack of strict as you already noted.
• Other things we can't see any code for.

I'm able to test this much (on 5.32.0):

# The sort of result that was no doubt expected:
$ perl -e 'use Data::Dumper; my $hr = bless {a=>1}, "H::R"; my $r = $h
+r; print Dumper $r'
$VAR1 = bless( {
                 'a' => 1
               }, 'H::R' );

# Reproduce output with stringification and embedded newline:
$ perl -e 'use Data::Dumper; my $hr = bless {a=>1}, "H::R"; my $r = "$
+hr\n"; print Dumper $r'
$VAR1 = 'H::R=HASH(0x800003b78)
';

# No bucket allocation ratio for me; also no strict to advise of probl
+em:
$ perl -e 'use Data::Dumper; my $hr = bless {a=>1}, "H::R"; my $r = "$
+hr\n"; print Dumper %$r'

# Problem advice when strict is used:
$ perl -e 'use strict; use Data::Dumper; my $hr = bless {a=>1}, "H::R"
+; my $r = "$hr\n"; print Dumper %$r'
Can't use string ("H::R=HASH(0x800003b78)
") as a HASH ref while "strict refs" in use at -e line 1.
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Bod, address the dot points above: there may be a solution in there. If that solves nothing, provide more code. Also, what Perl version are you using? (I seem to recall you had different versions on your local machine and your hosted server.)