ClojureCLR .NET 3.5 with-open trouble finding .Dispose

user=> (import 'Microsoft.Win32.Registry)
Microsoft.Win32.Registry
user=> (import 'Microsoft.Win32.RegistryKey)
Microsoft.Win32.RegistryKey
user=> (with-open [hkey (Registry/CurrentUser)] )
MissingMethodException Cannot find instance field/property/member name Dispose
.CallSite.Target (:0)
user=> (with-open [^IDisposable hkey (Registry/CurrentUser)] )
nil
user=> *clojure-version*
{:interim true, :major 1, :minor 5, :incremental 0, :qualifier "master"}
user=>