It's only a visual thing. When you use a popup with the option to show a second field. The target field display will show the second field. But the target field itself will ONLY contain the value of the first value list field, not the value from the second value list field. Put the target field on the layout again, but without a value list attached to it and you will see that with both drop-down and popup, only the value fo the frist value list field gets into the target field.
I've found it tricky to get the best out of drop-downs and pop-ups, and now generally use both on the same field. I've documented this here - doesn't directly address the point you've raised, but may be of use or interest to you.
So the displayed "data" in the actioned layout is just there for the user so it matches what they selected. The real data is not the "name" but the record SN.
I should have looked at the results in another layout. I am not used to such luxuries.