I am having the same issue.
I create a PDF in LiveCycle Designer ES2 as an A4 document with set margins.
Then I print it either from LC Designer "Preview PDF" or from Reader x and it rescales my PDF with extra margin space all around. This can become an issue for me as the printed versions need a set minimum quiet zone around the barcodes to allow for scanning.
The documents I am making are for use in browser based electronic medical record system across two hospitals, so individual PC solutions (cropping etc) will not work in this environment.
I am also creating PDFs on a custom page (eg all areas scaled up by 10% including margins), but the addition of the margin by Reader means it throws out the calculations I have accounted regarding the barcode quiet zones when the forms scales back using "print to fit".
It also scales objects that I have calculated to scale back from, lets say A4 @ 110% back to A4 @ 100%. EG a 11cm square should sclae back to the intended printed 10cm square to allow the placement of a sticker. It scales smaller due to Reader placing extra margin space and resizing based on that margin space.
Sorry to ride on this thread, but it looks like the cause of the problem is the same.