Not possible to select fields for export when using Custom Searches

When doing a custom search (on demo site 3.4.0 and on PTP's site that's using 3.4.1), I can't select fields for export.

I did a number of custom searches (proximity search, include/exclude, activity search) and when I choose action "Export Contacts" and hit "Go", the .csv file downloads immediately. I was expecting to get to select fields, but I never even get to that screen.

For example, doing a proximity search on contacts within 1000 miles of zip 94707 gets me 17 contacts. I can't choose which fields for these contacts to export.