Can't use portal to go back into Mines.

Cruel, Act IV, just entered the Mines. Found a Stone Altar, opened a portal to go back and get some talismans, and when I try to return through the portal I get the message 'You have not completed Cruel difficulty'. I can go back through the main entrance of the Mines no problem, I can return to my portal in the Mines and use it to go back to town, but I can't go back through the portal from town. If I go back into the Mines and open another portal, I can see two portal icons on my map, but I still get same message trying to return back through the new portal.

I took a screenshot, but it's just my character standing in front of a portal with the message displayed.

I've seen something like this problem mentioned with daily quests for Masters, but I didn't see anyone mention it outside of that context.

Quitting the game and restarting seems to have eliminated the problem.

Edit: Or not. The first portal I opened worked fine, but the second portal, opened on the 2nd floor of the Mines, suffers the same problem.