XamMultiColumnComboEditor behaviour when combining AllowMultipleSelection="True" and CustomValueEnteredAction="Add"

I have a XamMultiColumnComboEditor with:
ItemsSource="{Binding TestStrings}"

When I type in this control and add a value that is not in the underlying collection, it all works fine and it adds it to list as expected. 
However, why I try to add multiple values that are not in the list using the delimiter ";" the control clears the selection

For Example:

If my list TestStrings is { "a","b","c"}
And I type "d" into control, the value "d" is added and selected as expected because of the CustomValueEnteredAction="Add"

However, if i want to add "d" and "e", i will type, "d;e".  Typing this clears d from the text, removes d from selection and only selects e.  This is obviously not correct.

I am using version 14.1.20141.2108.

Is this fixed in any later versions of Infragistics?  Is there any workaround for this in my version?