View sorting becomes arbitrary with grouping field? The setup: 

A view that lists out nodes containing study abroad Program information. Its format is Unformatted List. There is a Grouping field of Country (which is a field on the Program content type). The list is sorted by Country (asc) and then Program title (asc).

There are exposed filters (via Better Exposed Filters) for a few of the fields from the Program content type... one of which is Country. These filters are exposed in a block that's included on the view page.

The Problem: 

When you perform a search via the exposed filter block with multiple Countries selected, the sort order seems arbitrary. The grouping (by Country) works, but the Countries are listed out of order... not alphabetical asc or desc... just arbitrary.

Worth mentioning: any other search using any of the other exposed filters, but not selecting any Country values, works fine.

What's going on here? Why does sort get wacky when searching by Country... which, coincidentally or not, is also the grouping field?
It seems that disabling "Reduce duplicates" on the exposed filter of the grouping field will bring the sort back in order. So, in this case, unchecking "Reduce duplicates" on the exposed filter, Country (which is also the grouping field) did the trick.