The negative says it all. A screw gate on this type of head makes no sense at all, particularly one without any kind of lock or secondary closure. I've always known the head was sketchy so I always double check my tighteners. On this particular instance I specifically remember checking all of the tighteners on my rig before picking it up, this was clearly a failure of the closure.
In the future I will avoid any ballhead with a screw gate closure.