When writing a PM you can add recipients via the link "find a member" button.
The member list opens in a seperate window, you can search and each member has a checkbox next to the name.
if you check multiple boxes and then press "select marked" the member list window closes and no members are added as recipients.
(All checked members should be added as recipients).
This happens on my phpbb forum, but also on the phpbb demo site (http://www.try-phpbb.com/32x).
I have tested both Chrome and Firefox, it happens in both.
Here are the exact steps to reproduce on the demo site:
1) goto: http://www.try-phpbb.com/32x
2) login as administrator
3) click private messages and "new pm"
4) click "Find a member"
5) check the checkbox next to administrator
6) click on "select marked"
7) observer that administrator has not been added to the recipients list
the button executes this code (in the onsubmit of it's form):
this.user is not assigned anything anywhere as far as I can tell.
My workaround is selecting all checkboxes via jquery and handing them to insert_marked_users instead of "this.user", code:
and the changed the onsubmit: