A summary of links comparing ODF (the file format native to LibreOffice and OpenOffice) with OOXML (as used in Microsoft’s Office suite): <http://courseweb.ischool.illinois.edu/~stanley8/LIS590DPL/standards/docformats.html>. Another reason why saving LibreOffice documents in MS Office format may cause formatting trouble (besides the usual inconsistencies that happen with MS Office formatting anyway) is that OOXML cannot actually represent all ODF information correctly.