Only masked profiles visible despite absense of view_participant_masked_profile permission

TAs in our CS 450 Fall 2018 course are unable to view participants names/info. It seems view_participant_masked_profile is on for them, however, "View participants' masked profile only" is not one of the permissions granted to the TA role. Tried adding and removing it and looked through and tested other permissions, but without any success. From the instructor role, I am able to see the participants info, but its not clear where the difference comes from that causes profiles to be masked. The list of permissions currently granted to TAs is below. cc @inducer @dzhuang
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Participation role: ta in cs450-f18

Participation role permission: batch_impose_flow_session_deadline for ta in cs450-f18
Participation role permission: view_analytics student for ta in cs450-f18
Participation role permission: update_content for ta in cs450-f18
Participation role permission: query_participation for ta in cs450-f18
Participation role permission: access_files_for public for ta in cs450-f18
Participation role permission: access_files_for unenrolled for ta in cs450-f18
Participation role permission: view_calendar for ta in cs450-f18
Participation role permission: access_files_for student for ta in cs450-f18
Participation role permission: send_instant_message for ta in cs450-f18
Participation role permission: edit_participation for ta in cs450-f18
Participation role permission: query_participation for ta in cs450-f18
Participation role permission: test_flow for ta in cs450-f18
Participation role permission: use_page_sandbox for ta in cs450-f18
Participation role permission: use_markup_sandbox for ta in cs450-f18
Participation role permission: preview_content for ta in cs450-f18
Participation role permission: view_analytics for ta in cs450-f18
Participation role permission: grant_exception for ta in cs450-f18
Participation role permission: reopen_flow_session for ta in cs450-f18
Participation role permission: recalculate_flow_session_grade for ta in cs450-f18
Participation role permission: regrade_flow_session for ta in cs450-f18
Participation role permission: end_flow_session for ta in cs450-f18
Participation role permission: impose_flow_session_deadline for ta in cs450-f18
Participation role permission: batch_download_submission for ta in cs450-f18
Participation role permission: view_grader_stats for ta in cs450-f18
Participation role permission: skip_during_manual_grading for ta in cs450-f18
Participation role permission: assign_grade for ta in cs450-f18
Participation role permission: view_gradebook for ta in cs450-f18
Participation role permission: view_flow_sessions_from_role student for ta in cs450-f18
Participation role permission: issue_exam_ticket for ta in cs450-f18
Participation role permission: access_files_for in_exam for ta in cs450-f18
Participation role permission: access_files_for ta for ta in cs450-f18
Participation role permission: view_hidden_course_page for ta in cs450-f18
Participation role permission: set_pretend_facility for ta in cs450-f18
Participation role permission: set_fake_time for ta in cs450-f18
Participation role permission: impersonate_role student for ta in cs450-f18
Participation-participationrole relationship: Participation_roles object (12410)
Participation-participationrole relationship: Participation_roles object (12370)
Participation-participationrole relationship: Participation_roles object (10187)
Participation-participationrole relationship: Participation_roles object (10186)
Participation-participationrole relationship: Participation_roles object (10185)
Participation-participationrole relationship: Participation_roles object (10184)
Participationpreapproval-participationrole relationship: ParticipationPreapproval_roles object (5380)
Participationpreapproval-participationrole relationship: ParticipationPreapproval_roles object (5379)
Participationpreapproval-participationrole relationship: ParticipationPreapproval_roles object (4839)
Participationpreapproval-participationrole relationship: ParticipationPreapproval_roles object (4838)
Participationpreapproval-participationrole relationship: ParticipationPreapproval_roles object (4837)
Participationpreapproval-participationrole relationship: ParticipationPreapproval_roles object (4836)
```

Reproduce the difference between the TA and instructor roles in the CS 450 course, focusing on the view_participant_masked_profile permission and the listed TA permissions. Trace how participant-profile visibility is determined for each role. Done means TAs can view participant names and information according to the intended permission, with the relevant behavior covered by a regression test.

Written by the indexing model from the issue text.