It's not that. There is a message. I didn't notice that because it shows below the screen (you need to scroll down to see it): "Account requires 10x the account creation fee in Steem Power (approximately 300 SP) before it can power down."
Right now I have just 301 SP, so it looks like they're trapped.
RE: I can't power down my Steem Power anymore. That doesn't smell good.