Are you sure the compilers are the exact same version?
If the systems do not have identical processors, it may just be the result of slight differences needed for optimization, etc. I've seen lots of differences in optimization between differing processors of the same architecture.
Typically all compiled code will differ on each individual machine. The only way to assure that it will be identical, is for both systems to install a precompiled ojbect onto their systems.
What is the issue exactly? Is there some reason why you need both objects to be the same size?