Portals aren't exactly the most common method of transportation, so it's hard to say if it's intended to work like this or not. But-- as of right now, it's definitely one-way. Some of us were running into it earlier to find out, but it's basically just a wall now.

[All of the portals seemed to be that way, so she figures that must be either intentional or a city-wide sort of failure. Which makes her think this might be some kind of technology rather than magic.]