ASP.NET Wizard and Framework 3.5

After upgrading our web application to .NET 3.5, we noticed a strange issue with the Wizard control. Usually, after restarting IIS and loading the page with the control, the left navigation bar is not displayed. Clicking this page again will fix this problem. It is also visible in dev environment, although it is intermittent and I don't have a reproducible sequence of steps. Has anyone else faced a similar problem?