[Deceptor]

From what tests I've been able to do, the prompt should show on failure. It's possible the error haults this from happening, try the following change to see if it resolves your issue:

Open: ./includes/class_activecache_methods.php, Find:

		for ($x = 0, $total = xcache_count(XC_TYPE_VAR); $x < $total; $x++)
		{
			if (xcache_clear_cache(XC_TYPE_VAR, $x))
			{
				$any = true;
			}
		}

Change this to:

		for ($x = 0, $total = xcache_count(XC_TYPE_VAR); $x < $total; $x++)
		{
			if (@xcache_clear_cache(XC_TYPE_VAR, $x))
			{
				$any = true;
			}
		}

Find:

if (!isset($_SERVER['PHP_AUTH_USER']) && $x < 1)

Change this to:

if (!isset($_SERVER['PHP_AUTH_USER']))

Save and upload, let me know if this resolves the issue for you