Whenever dispensers place water above soul sand and recollect it, the updraft effect doesn't go away. This may not seem like a big deal, but it is. I use dispensers with water buckets for an automatic nether wart farm. When the updraft effect is still there, it prevents me from placing nether wart for some reason. It physically won't let me place nether wart on the soul sand with the updraft effect on it. The picture shows what this looks like.