I have configured the SSRS 2008 for Basic Authentication exactly following instructions in this article letter-by-letter:

How to: Configure Basic Authentication in Reporting Services

Everything works: (saving, opening, browsing report models, etc.) except Preview in the Report Builder 2.0 - I receive "The request failed with HTTP status 401: Unauthorized." when I try to preview the report.

Is this a bug in Report Builder 2.0 with Basic Authentication or am I misconfiguring something?