When building a fort, there seems to be a game-breaking issue where the pathfinding determines that areas of the fort are not "reachable" any more, as if some kind of barrier or blockage separated the areas. Nothing is actually separating the areas though.
See this image: http://imgur.com/7RmIMsF
Here, you can see some dwarves who've gotten stuck. The cursor here is me trying to place a table (for the purposes of demonstration). You can see the cursor is yellow, indicating a valid spot.
However, in this image, we can see a problem: http://imgur.com/wUrurnu
In this image, I moved the cursor exactly one spot to the left. And now it's invalid. No time has passed and I haven't done anything funny in between, it is directly after the first image. The game is complaining here is that there is "no access to table". Somehow, the pathfinding seems to think that the square to the right is fine, but the one to the left does not have a direct path to the stockpile (there absolutely is, as you can imagine).
This seems to clear up if I save and reload.
The issue is caused by certain types of construction. As you can see from here, I've built a track made of logs and when a dwarf builds a track, all the squares surrounding it become cut off from the rest of the map. Dwarves who build a track then become frozen as "No Job" until I reload the save.
Constructed floors also do this.
This also happens in the Masterwork pack (for me at least) but doesn't happen in the latest vanilla DF.
Anyone have any ideas what's up? I'm tempted to believe DFHack may have something to do with it as I didn't use it on the latest DF, but I'm damned if i know what it might be; DFHack doesn't report any issues when this issue occurs.