--Create a project > project task > assign a user to the task
--Go to the project task > create a time card for the user assigned
--Approve the time card
--Expense line generated on project task
--An expense line on Project is also created which does not have time_card field populated.
Working as per the design.
While approving a time card of a project task, it creates an expense line having reference to time card.
This happens through Time Card's BR 'Process time card'.
Now if the system property 'glide.cost_mgmt.process_task_top_task' is enabled(i.e. value = true), then through expense line's BR 'Process Top Task Parent' it creates an expense line for its parent (i.e. project here). For processing expense line to top task, it does not have reference from where it is generating, wether through time card or something else. So, it always have no reference to time card.