Search doesn't update results as expected

I don't think the search results are updated when they should be.

Reproducing:
1. I use the Search option (top right on default toolbar), my default field is 'From'.

1. I enter an email (FF) and do see the results filtered on that email (correct!)

2. I click the + button to add a search criteria, and change to a Subject search and enter some text (SS)
   3.1. At this point I assumed the results would filter to email's from FF with subject SS. However, the results don't change.

3. I uncheck the 'From' criteria
   4.1. I do see the results update based on the subject criteria.

4. I then recheck the From criteria
   5.1. I see my original expectation -- results filtered to those from FF with subject matching SS.

The state of the UI is the same at points 3.1 and 5.1, but there are different results. I expect the results shown at 5.1 to be present at 3.1.