Image_captcha unique URLs make cache_menu table grow a lot

image_captcha path is generated by code:
$img_src = check_url(url("image_captcha/$captcha_sid/" . REQUEST_TIME));
For every generated captcha image, there will be executed menu_get_item() function, which will cache router item for every $img_src path;

 $cid = 'menu_item:' . hash('sha256', $path);
 cache_set($cid, $router_item, 'cache_menu');
 

Of course these menu_item cached records will never be reused. On high traffic pages cache_menu table grew over 800Mb.

Solution can be simple:
$img_src = check_url(url("image_captcha/$captcha_sid/", array( 'query' => array('ts' => REQUEST_TIME) )));