Please refer to the attached sample project and follow the steps from the gif file.

1) User does a search operation

2) BackgroundWorker does its task and finishes at some point, then set defaults to select the first result.

3) User selects a different result row.

4) Selected record still indicates and points to the first result.

Workaround:

Me.RadMultiColumnComboBox1.EditorControl.MasterView.TableSearchRow.AutomaticallySelectFirstResult = False