When a student starts working in another window on a test with Force Completion set, the test is automatically saved as complete. While the student can go back to working in the original window, anything saved is simply discarded.
In this scenario, your student is able to return to the original window, mark additional answers, and make screen captures until the local ("client-side") timer ran out. Those additional saved answers will simply be ignored by Blackboard Learn.
January 13, 2015