Foreign GPAs aren't re-calculated. The CAS report will show the original GPA you received from the foreign institution, and this GPA is not included in the process of calculating your LSDAS GPA.
Logickills - unfortinately, even if LSAC accepts the transcript from your semester abroad, it won't affect your LSDAS GPA since foreign GPAs don't count as part of your LSDAS GPA. You should send your transcript anyway (if not to LSAC, then to individual schools) - if it's sent as part of your application package, the schools you apply to may consider the grades from your semester abroad, even if LSAC doesn't.
Tome - Your situation is similar to mine, only I spent a year 'abroad' in Canada. I believe the GPA from your semester in the US will be calculated as your LSDAS GPA (if they accept transcripts from single semesters), and your BA and MA GPAs will only show up in the CAS report as stated on your original school transcripts. But in your case, law schools will generally look at the CAS reports rather than your LSDAS GPA.
Hope this helps!