array_walk only partially removes matches

Question

Ran into a weird situation were using array_walk() will only partially remove matches from my method, not certain exactly what is going on. I am currently using PHP v5.6.4. The issue almost seems to be that it is only removing every secondary match.

The kerning function

private function strip(array $exceptions)
{
    array_walk($this->hosts, function($v, $k) USE ($exceptions)
    {
        foreach ($exceptions AS $exception)
        {
            if (preg_match("/{$exception}/i", strtolower($k)))
            {
                unset($this->hosts[$k]); break;
            }
        }
    });
    print_r($this->hosts); die;
}

Answer 1

Quoting from the PHP docs

Only the values of the array may potentially be changed; its structure cannot be altered, ie, the programmer cannot add, unset or reorder elements . If the callback does not respect this requirement, the behavior of this function is undefined, and unpredictable.

my emphasis

Answer 2

This worked in conjunction with the information provided by Mark Baker, thanks Mark.

private function strip(array $exceptions)
{
    $this->hosts = array_filter($this->hosts, function ($k) USE ($exceptions)
    {
        foreach ($exceptions AS $exception)
        {
            if (preg_match("/{$exception}/i", strtolower($k)))

                return false;
        }
        return true;
    }, ARRAY_FILTER_USE_KEY);

    return $this;
}