So, I boot into Pico-8 fullscreen, do stuff, and type "shutdown". However, instead of shutting down Pico-8 and returning me to Raspbian Jessie (latest version), it just freezes up. Anyone else experiencing this?

That's a know issue, if started by a (shell) script pico-8 does not exit when shutdown is called on the Pi (need to be tested under Linux btw)