I believe this might be already fixed for the 1.6 but just in case -

For the FTB Unleashed - (BiomesOPlenty-0.5.7) if Biomes are installed and you have placed the spring water in a BC tank the world will crash if you are close enough to the tank.

I believe this is a backport to work with the Unleashed pack.. but just in case... :)

Yeah, it is fixed. The reason it is broken isn't our fault though, just a matter of a lack of code with the 0.5.7 backport (not done by us).