embedded absolute urls change to relative urls

I manage a multiblog site (several blogs, one domain name, each blog in subfolder). I have one out-of-town non-techie blogger who has problems with links in posts: Within a post, he links to previous posts in his specific blog, but the links end up going to a different blog because somehow the links become relative. He uses Word on a Mac both to write his posts and insert links. He then copies and pastes the text with links into WordPress. I’ve checked the links in his Word documents — they are absolute urls and work correctly. But when I view the code in the browser, I see they have become relative urls. The url is truncated down to “../?p=123” instead of “http://domain/specific-blog/?p=123” as found in the original Word file. And “http://domain/?p=123” is on a different blog, of course (or just “file not found”).
Even more puzzling, if I go into WordPress, using the edit link icon in the visual tab, I find the link is absolute (and correct)! There is nothing to change, and simply clicking “update” solves the problem.

Does anyone have an idea of what the problem is? Could it possibly be his Mac, which he says is new? I’m on a PC and cannot recreate the problem using his Word files (the links always work when I post). Any insight would be much appreciated!