Wrong search results when combining smart and non-smart groups in a single search

When you run an Advanced Search for members of multiple groups, one of which is a smart group and one of which is a non-smart group, the results only show members of the smart group.

Reproduced on 4.7.15 demo site (WordPress):

1. Create a smart group of, say, people with a specific gender
2. Go to Advanced Search
3. Include this group, along with a non-smart-group (say, 'Newsletter Subscribers')
4. Search. The results only show members of the Smart Group

(this worked ok in 4.6.x)