I don't think that is swamp water spreading, but one of those strange shadow bugs which makes it look like that.
If you look closely when I'm standing in the water only IT is getting darker and not the block beneath it. There are no blocks being built above or inside the water (obviously) to make a shadow appear, but it isn't in the changelog so you could be right.
I think this was because in 1.2(.2) the clouds would cast shadows, it was done on purpose (it was on the official change list) and skeletons and zombies would hide in the shade to survive, but of course that made it very ugly having shadows everywhere (ESPECIALLY when smooth lighting was not on) and the skeletons and zombies pretty much ALWAYS survived the daytime, so they removed it in 1.2.3
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ragnarock200: awesome, are those things with the creeper faces pistons or furnaces
Snowey1994: There dispensers