Ah, it's simple.  So when you do 

```
if( this.selectable )
   this.setSelectedModels( oldSelectedModels, { by : "offset" } );
```

In the case of a single selection it uses the index of the original selection to set the item now at that index as selected.

In the case of the multi-selection it uses the index of the original selections to set the items now at those indexes as selected.  The issue is that the tests don't indicate that it is the desired behavior.  In the case of the multiselect the selection should shrink, so that is why I put in the test, reset the selected items, etc.

So either we change the expected behavior of removing items from a multiselect in regards to how the selection is modified or we just trigger the selectionChanged event from this location... or if you have another idea, I'm all ears.