If you have two or more instances of GridViewItemsSourceProvider that you switch at runtime, their columns get cleared on the second switch. This happens because when the ItemsSourceProvider of RadMultiColumnComboBox changes, the columns of the old GridViewItemsSourceProvider get cleared. So, you cannot use the old provider anymore, unless you add the columns again manually.

To resolve this, use a new instance of GridViewItemsSourceProvider, each time you change the ItemsSourceProvider property.