Some people will sue McDonalds when they spill hot coffee on themselves. Some people will sue a building owner when they trip and fall. Some people will sue to try to get back their IP that they clearly gave away to the public domain. We can't stop stupid people from being stupid.
Only a (stupid) lawyer could love a copyright loophole like the one described in the article. But we can't live in fear of these people. If somebody dedicates their work to the public domain, we have to trust that they will keep their word. Sometimes they don't, but sometimes people don't honor legally binding contracts, either.