Starting this evening I'm seeing terrain squares with big red exclamation points in them and the message "OPEN Costs one move point to enter. Doesn't block sight." when I right click them. I first encountered them in the level 9 arena module so I thought perhaps it was unfinished content or perhaps part of the encounter but now I'm replaying a level 2 module and they are there and they weren't when I played before. I searched the forum and couldn't find anything about them so I didn't know if this was a known bug or what the deal was. Other than that I'd just like to say I'm loving the game and beta. I've been following this game for probably a year now so getting into beta and being able to play it has been a treat.
This is likely an issue with loading the graphics for the terrain. There have been a few mentions of it, but seems to be random. If this happens to you every game I suggest you check in the board tile bug thread.
Update: When I was getting the tiles it was during one play session and I never reloaded the game. So far today I haven't seen them.