I seem to have accidentally found a bug with water. I made a pair of channels on a z-level, lets call it z = 1, dugging into z = 0. The river is on z = 1 and z = 0 as well. The idea was to divert water into one channel, and have them both fill up. Thus the channels are connected to eachother via a tunnel going from under one to under the other on z = -1. Because of water pressure, the water was supposed to rush into channel 1 on z = 0, through the tunnel in z = -1, and up into channel 2 on z = 0.
What happened was water properly filled channel 1 on z = 0 and filled the tunnel on z=-1, but will not come back up on the other side. I even tunneled out where the water was supposed to come up, but all it does is show the dark-blue 7 on z=0, representing 7 units of water directly below. Channel 1 on z = 0 is full, and is DEFINITELY connected to channel 2 on z = 0 via the tunnel on z = -1 (again, I can see the dark-blue 7 under that channel where water is supposed to come up). The water just will not flow up.
I can't seem to figure out how to post images that do not have a web address, so if you want to see the pictures I exported, tell me or tell me how and I will post them or e-mail them.
I imagine that whatever is causing it was originally meant to remove the infinite water trick that used-to exist, but this problem seems to arise, now. In hindsight, though, I am glad it is there, because I had never gotten the old infinite-water trick to work, and I imagine that if it still existed I would've just flooded my fortress.