Changing the data source of the affected layer by going into Layer Properties->Source tab, clicking on Set Data Source and then selecting another file will release the lock. So the user can go into Windows Explorer, find the file(s) in question (make sure to take all of the files *.shp, *.xml, *.prj, etc.) and copy and paste them to another location. Then, change the data source to this newly copied file. The file handle will be broken. It's not pretty but it works. User notes he cannot get this to work reliably in code, and thus requested that the issue be raised in status.