I think that this is a major bug. After rendering a clip I have to exit Vegas and restart to see the rendered video in exploler. It is just mine mess-up?
Vegas seems to cache the information in the explorer pane instead of updating it when the contents change. Click anywhere in the explorer window to give it focus and then press F5 to manually force an update. It may take a few moments, but it's faster than shutting down Vegas and restarting.