Classic Time Card not saving hours from new assignment mid period

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We have employees who are assigned a new position mid pay period. They already have hours added to their time card for the previous assignment, but when they add hours to the time card for the new assignment and save their time card the time in/out is added to the first assignment and the second assignment is removed from the time card. For example, Wilma Flintstone has an assignment for Job A. She worked job A on Monday and Tuesday. On Wednesday she was assigned Job B so she adds a new line on her time card and enters her time