If this is the case, I have been REALLY lucky with the design of my pump stack. Are you all sure about this? Do yall have a ground tile to support the pump? If not I recommend you put one in.
It's a typical head-over-tail pump stack design. The bottom-most pump has a ground tile and the top-most pump is hanging off a gear assembly. All the other pumps must hang, because I channeled away the ground tiles to let power pass through. I'm following the instructions on the wiki, so I don't think that's the problem.
As Starver said, it probably lets me place and build completely unsupported pumps because they are "supported' by other placed (but not constructed) pumps. Once built, they collapse because of lack of support.
What has been frustrating is that the unsupported pumps don't collapse immediately after construction. They stick around until i've built other pumps that rely on them for support before collapsing, bringing down the whole chain. I can even add a support to a constructed pump in the form of a grounded gear assembly, and it still collapses, taking the gear assembly with it.