I'm not sure it's a windows issue Craig as I can do drag and drop in other apps running as admin or not. Regardless it's easily resolved... Don't run Sonar as admin as you say (it should be avoided), if you have plugins that rely on it give the registry settings for the plugin appropriate permissions (google search forums for further details on how to do it). Registrations may need Sonar to be run as admin as a one time operation (such as Dim Pro).
Oh and I wish they would totally revamp the browser to be more like NI. It needs work.
Cheers..