Originally Posted by FastJake

Different thickness spacers on the same cassette is one of the dumber things Campy has done recently (but not a huge deal.) Fortunately, you can avoid this confusion and a dozen other issues by using Campy 10-speed brifters with a Shimano 8-speed system, because the cable pull is exactly the same. Though I've moved onto downtube shifters now and have little use for brifters.