I have exactly the same problem, can't save exactly that section. Any other section, no problem.
Fresh install of 1.6.1.5 with custom theme.
Moreover, if i edit the translation file with an editor then i update the translation in back-end, all fields gone empty again despite the fact that they showed translated when i did a refresh to page after rewrite edited file in ftp...
Edit:
i have on my shared host:
suhosin.request.max_vars = 5000 suhosin.post.max_vars = 5000