We encounter a strange problem when making web service calls via SoapHttpClientProtocol in .Net. We have UseDefaultAuthentication set to true. In Internet Explorer an account with less permissions has saved passwords (and in fact created a pass-through). When the web service calls are made under an account with more permissions, the call to the web service does use the previous account.
When the IE settings are cleared, the web service call uses the actual account.
Any ideas about how accounts caching, IE, IIS and web service calls may react on each other? What is the primary source of the problem?