Here's another example:

# foo.pl
use strict;
use warnings;

require 'bar.pl';

frobozz( 2 );

__END__


# bar.pl
use strict;
use warnings;

{
  my $x;    # same thing with "my $x = 'whatever';"

  frobozz( 1 ) unless caller;

  sub frobozz {
    ( $x ) = @_;
    print 'NOT ' unless defined eval( '$x' );
    print "OK\n";
    quux();
  }

  sub quux {
#    $x = $x;
    print 'NOT ' unless defined eval( '$x' );
    print "OK\n";
  }
}

1;

__END__
[download]

If one runs foo.pl, the output is

OK
NOT OK

...meaning that frobozz sees $x but quux doesn't. If one uncomments the commented line in quux or runs bar.pl directly, the output is

OK
OK

(This is true for both 5.8.6 and 5.8.8 on Linux.)

After re-reading the docs on eval, I can't see how a programmer can be expected to predict this behavior. Therefore, it is, at the very least, a design bug, IMO.