Thanks Ladies ...
yes, I had checked to make sure the PP printed to the correct size - I checked both the 1" test square and the size of the whole block (both on paper and after piecing).
I'm convinced that the problem is that I'm using one method (scant 1/4" seams) on one half, and another method (true 1/4" seams) on the other half ... it's not going to work! I suspect that this is always a problem when marrying a PP block to a block made with scant seams. DUH!
I'm making another block right now. I've made the PP unit just a smidge larger. Will see if this works.