Images not being rewritten to mapped domain

The question pretty much sums it up. I have a multisite installed at, and a subsite (in subdirectory mode), which has two domains mapped:
- (primary)

Most of the site seems to be getting rewritten properly, but most images (and some other bits) seem to point back to www-admin. Since I have and served by different hosts, this screws things up.

Can you tell me what I'm doing wrong?