RCDC UocCommonMultiValueControl seems to filter duplicate values!

I am experimenting with the UocCommonMultiValueControl and multi-valued attributes.

I entered the following in the multi-line text box shown on the screen:

Value1

Value2

Value10

Value 10

Value 12

and when on the "Submit" page showed   Value1;Value2;Value10;Value12

Is this filtering out duplicate values by design? This behaviour is not documented.