$array["inf"] など

Perl 5.8

$ perl -Mwarnings -MConfig -e '@ARRAY = (1, 2, 3); printf "%vd\t%s\t%s\t%s\t%s\t%s\n", $^V, $Config{archname}, $ARRAY["inf"] || "false", $ARRAY["-inf"] || "false", $ARRAY["nan"] || "false", $ARRAY["string"] || "false"'
Argument "string" isn't numeric in array element at -e line 1.
5.8.9   x86_64-linux-thread-multi       3       1       1       1

Perl 5.14

$ perl -Mwarnings -MConfig -e '@ARRAY = (1, 2, 3); printf "%vd\t%s\t%s\t%s\t%s\t%s\n", $^V, $Config{archname}, $ARRAY["inf"] || "false", $ARRAY["-inf"] || "false", $ARRAY["nan"] || "false", $ARRAY["string"] || "false"'
Argument "string" isn't numeric in array element at -e line 1.
5.14.2  x86_64-linux-gnu-thread-multi   3       1       1       1

Perl 5.18

$ perl -Mwarnings -MConfig -e '@ARRAY = (1, 2, 3); printf "%vd\t%s\t%s\t%s\t%s\t%s\n", $^V, $Config{archname
}, $ARRAY["inf"] || "false", $ARRAY["-inf"] || "false", $ARRAY["nan"] || "false", $ARRAY["string"] || "false"'
Argument "string" isn't numeric in array element at -e line 1.
5.18.2  x86_64-linux-thread-multi       3       1       1       1

Perl 5.20

$ perl -Mwarnings -MConfig -e '@ARRAY = (1, 2, 3); printf "%vd\t%s\t%s\t%s\t%s\t%s\n", $^V, $Config{archname}, $ARRAY["inf"] || "false", $ARRAY["-inf"] || "false", $ARRAY["nan"] || "false", $ARRAY["string"] || "false"'
Argument "string" isn't numeric in array element at -e line 1.
5.20.0  x86_64-linux-thread-multi       3       false   1       1

http://search.cpan.org/dist/perl-5.20.0/pod/perldelta.pod#Better_64-bit_support で動作が変わったのですかね。