ASP.NET theme not rendering correctly

Question

I have a small web application which uses themes. The themes work on host, so on preinit, if the host = a, load x theme, if the host = b, load y theme.

In my code this

Answer 1

Yep, it is on page preinit.

I think it is to do with forms authentication. If I view (not debug) the login page, it picks up the localhost theme and everything is displayed correctly. The login control is in the middle of the page, as it should be, etc.

But if I debug the page and, as you'd expect, the login page is the start/default page, the login control appears to the left as it does when I deploy and the source indicates the css for the appropriate host has been picked up - only when I debug, there is no style applied until I login.