This is resolved in Raiser's Edge 7.96 patch 2, applied to databases in Blackbaud Hosting Services in January 2017 and planned for download availability in February 2017. For further updates on releases as they become available, please see our Community Release page.
Alternative solution if using a previous version:
1. Click on the column you want to sort by on the Participants tab
2. Save and close the event
3. Reopen the event - the Particpants tab is sorted by desired column