OS X does not use Frame::setPrinting, since it still has its own WebKit method. The cross-platform method was copied from it, and I noticed while mucking around in the printing code that it contains an error. Subframes are not supposed to receive the page size or lay out to the page size. The Mac method just passes 0 for all the numbers to child frames, so I will change the cross-platform method to match.
Created attachment 68244 [details] Patch
Fixed in r67956.