Recently there have been some hotfixes released to address Vault 2012 API issues.
API Log In Hotfix
This gives you a new Autodesk.Connectivity.WebServicesTools.dll which contains a WebServiceManager that doesn't log out at incorrect times. I still recommend using the bugfix credential classes because, if there are multiple extensions, some of them may contain the old DLL. There is no way know which version of WebServicesTools gets loaded at runtime.
Because the SDK is distributed as an installer, the hotfix updates that installer. You need to re-install your SDK to get the updated DLL.
API Working Folder Hotfix
IExplorerUtil had an issue with the GetWorkingFolder function which caused it to return the incorrect path. That issue had a ripple effect causing GetLocalFileStatus and DownloadFile(File, Folder) to also be incorrect. This hotfix corrects the problem, so all 3 functions should work properly now.
The fix is in one of the Vault Explorer DLLs. The SDK itself does not get updated. If you are using IExplorerUtil, you do not need to change anything, nor do you need to re-compile code.