Images not being rewritten to mapped domain

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

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 www-admin.cloudtp.com and http://www.paaslane.com served by different hosts, this screws things up.

Can you tell me what I'm doing wrong?