Old Hopper Minecarts have Enabled:0b/do not gather items

Hopper Minecarts placed in versions before 15w37a do not gather items as they did in the prior versions. If the hopper minecart is broken and placed again in 15w37a it will then work as expected. I suspect that previously created carts do not have the enabled flag set. (As that flag did not exist before 15w37a.)