This is string eval and that's the reason why string eval is considered bad practice (generally).

$ cat x.pl
#!/usr/bin/perl -Tw
use strict;
use warnings;

my $x = "016";
my $y=$x * 10;
print "y=$y\n";

$y = eval( "$x * 10" );
print "string eval evalled 016 * 10 , y = $y\n";

$y = eval { $x * 10; };
print "block eval evalled 016 * 10 , y = $y\n";

$ ./x.pl 
y=160
string eval evalled 016 * 10 , y = 140
block eval evalled 016 * 10 , y = 160
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Avoid string eval. The reasons why you see the numbers you do are well explained in the previous replies. Use block eval and the problem (the apparent inconsistency) disappears and you don't have to think about unexpected stringification.