# the fix:
@items = grep {
    my $keep = !exists $del{$_};
    $i++;
    $index -= ($i < $index) unless $keep;
    $keep
  } @items;

# the results
Benchmark: timing 100000 iterations of BrowserUk, dpuu...
 BrowserUk: 13 wallclock secs (13.72 usr +  0.00 sys = 13.72 CPU) @ 7288.63/s (n=100000)
      dpuu: 10 wallclock secs ( 9.88 usr +  0.00 sys =  9.88 CPU) @ 10117.36/s (n=100000)
             Rate BrowserUk      dpuu
dpuu      10117/s       39%        --
BrowserUk  7289/s        --      -28%