Further to toolic's post, the change seems to have occurred between 5.8.9 and 5.10.1.

c:\@Work\Perl>perl -wMstrict -le
"print qq{perl version $]};
 ;;
 my %h  = qw(a aye  b bee);
 my $hr = \%h;
 ;;
 print ${ %{$hr} }{a};
 print ${ %h     }{b};
"
perl version 5.008009
aye
bee

c:\@Work\Perl>perl -wMstrict -le
"print qq{perl version $]};
 ;;
 my %h  = qw(a aye  b bee);
 my $hr = \%h;
 ;;
 print ${ %{$hr} }{a};
 print ${ %h     }{b};
"
perl version 5.010001
Can't use string ("2/8") as a HASH ref while "strict refs" in use at -
+e line 1.
[download]

Checking perl5100delta and perl5101delta reveals no explanation for the change.

Update: Note that similar syntax works/doesn't work for arrays:

c:\@Work\Perl>perl -wMstrict -le
"print qq{perl version $]};
 ;;
 my @ra = qw(zero one two);
 my $ar = \@ra;
 ;;
 print ${ @ra  }[1];
 print ${ @$ar }[2];
"
perl version 5.008009
one
two

c:\@Work\Perl>perl -wMstrict -le
"print qq{perl version $]};
 ;;
 my @ra = qw(zero one two);
 my $ar = \@ra;
 ;;
 print ${ @ra  }[1];
 print ${ @$ar }[2];
"
perl version 5.010001
Can't use string ("3") as an ARRAY ref while "strict refs" in use at -
+e line 1.
[download]

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