When you use a Bucket of Milk in the world (like spawning a water source) the quarry keeps drinking it instead of doing it's job. Kinda funny because I like milk too but that's crazy. XD

I'd be thirsty too after eating mouth fulls of cobble and gravel :P

Vanilla minecraft doesn't have milk as a placeable fluid. It could be the mod's you're using that added that fault, or it could be the Quarry, since it goes fine through any other liquids. My guess is it's the milk's fault.

XD
It's #3135 on NEI, MineFactory reloaded. Maybe add an exception to the digging protocol for that item? :)

You would be better reporting this to MFR, they're on Github too.

https://github.com/powercrystals/MineFactoryReloaded

Buildcraft scans all blocks for supported types of Fluid Blocks, if MFR fluids don't work then its not using any kind of accepted standard from either Forge or Vanilla. And there really isn't a compelling case to special case support.