Yeah...this has been happening for a while. That amount of balls is actually pretty low. I've been down there before and it's nearly 100% coverage...you could walk across them almost from one end of the park to the other.
It's hard light glitch in clipping combos if enemy die while encase animation is fading in and also can happen if enemy just before it complete the break out animation , tennis balls will stay in phase instance until server reset if left or if you pick them up and use melee they will break , Glitch can also happen out side central city zone with other encase powers too like freeze block ,I've expierenced the glitch in spectral zones east in China town , antimonitor event and enemy in doomsday metropolis also.
