I have an Austin xl. I had that happen once almost 4yr ago. It's not normal no but it does happen for a couple reasons. One maybe the ash pot was full of ash before you fired it up. Two you could have a controller issue that is causing it to continue to feed pellets. Three you might not be starting the grill and shutting it down properly. And four which was my issue.......sometimes it just happens lol. If it's a common problem though then it's a problem. Give pitboss a call. Their customer service and 5yr warranty is awesome
As mentioned make sure the ash is cleaned out of the firepot, start up with the cook chamber open, set it to 300-350F, close when the first cloud of smoke dissipates, allow to preheat for 15 min before turning down to whatever temp you normally smoke at. If you're going really low, drop the temp in two steps rather than jumping from 300+ to 200F or lower. Check the p-setting to make sure the feed rate isn't too fast or too slow.
How long had the cooker been running when it malfunctioned? Did this happen in the middle or soon after startup?