Sparky H

I have a single variable speed system operating 3 zones (added on). In the Summer, when all zones are operating and all room vents are open, the bypass damper pours cold AC into the crawl space. I thought the bypass was only to open up if too much pressure was detected. So why would it be open. ? The crawl space seems to be cooler than room temperatures through the home. Is this normal and what should be expected?