SSRS Web Part Page - HTTP 400 Bad Request

I have several pages that have a single instance of an SSRS ReportViewer web part. Switching between pages or simply refreshing the page adds a new Reserved.ReportViewerWebPart.axd request cookie. Eventually the request header exceeds the maximum size and an HTTP 400 (Bad Request) is returned. Has anyone come across this problem and is there a way to get the web part to clean up after itself and delete its old cookies?