As it currently stands, private towns are in fact not private, unless you are not in a nation (which makes little sense due to the large plot bonus). This can lead to completely unnecessary bans and cause general confusion for players who do not want anyone but their town members to be allowed into their town. When people make their town private, they generally don't intend for random people to be able to get in. Because this would need to be done outside of Towny, it might be easier to get it out there that people actually can go to private towns if these towns are in a nation with other people. This needs to be clearly stated in the rules, because as it stands right now, it can lead to terrible circumstances. It could also be told to players when they run the command /t set public that "Warning: Members of your nation can still access your town" or something of the sort.