I experienced a similar error - when I add an item to the combobox's datasource, the display in the collection turns to "AssemblyName.ClassName". Here's how I overcame the bug:

cmbStudyTracks.DataSource = Nothing
cmbStudyTracks.DataSource = _studyTracks
cmbStudyTracks.DisplayMember = "Name"
cmbStudyTracks.ValueMember = "ID"

Works fine now.