In 39b, I had just finished building a giant construction. There was a pump tower inside, and I wanted to rig up some hatches to a lever for it. So while the hatches were being built, it was winter, so I dug down into the brook ice so I could attempt to dam it up further back. This failed, however, and I lost my miner/mayor in the process. I also set up the lever. Somehow my dungeon master got ontop of the lever, and was unable to move (constantly pathfinding ?) I removed the lever, but it didn't work. So I deconstructed the tile he was on, he fell through unharmed and I let him go. I attempted to build a few pumps around the area I wanted to wall up, but I noticed that the dwarves kept suspending one. So I look at my announcement screen, and they canceled it because they could not find the path, despite being able to get to the area. They also canceled subsequent lever constructions, and my Dungeon Master has dozens and dozens of pathfinding errors related to him getting equipment, as well as many other dwarves claiming a water source had vanished (when it hadn't, they had a drunking zone over a running brook, the winter's freeze was short (a day or so)). I tried to rebuild the lever in several places in the tower and around the map, but I just kept getting the suspension due to pathfinding error.
After updating to 39c, the problem still exists.
Long story short:
1. Cannot build anything, dwarves cancel it due to pathfinding
2. Cannot drink from brook (possibly can, but creates a LOT of pathfinding errors)
3. Dungeon Master cannot get to equipment he is trying to get, walks back and forth in a small area.
Update: Other bugs I remembered:
Statues and stones sometimes stay hovering in the air when the wall underneath them is deconstructed.