private.php newpm sendmultiple
 

I've a custompage with a form submitted to private.php with do=newpm that doesn't seems to work anymore with vbulletin 3.8.
We're used to select from this page multiple recipients for the private message filling a sendmultiple[] array with users id, but this variable doesnt seems to be understood from private.php, how to do that with vbulletin 3.8 ?
thanks!