I define a fixed work task, work is 16 h. I assign a resource Bob to work 100% on this task. The task duration is automatically set to 2 days. Since I figure out Bob won't have full time to spend on this task, I double click on the task to add Alice to the resources. I assign Alice to work 50% time on the task and change Bob from 100% to 50%. When applying the change, duration automatically changes to 2,67 days. Why? Two persons are working on a 16 h fixed work task, each with 50%. Why is there 0,67 days more scheduled than needed?
In case in the same task now I delete all resources and click OK and then insert resources again, now for Bob and Alice I assign 50% availability at the beginning, the calculation is correct. 2 days needed for the task to complete. No other changes were made - just resources deleted and entered again.
When the problem is present and I check the Team planner, I can see that Bob and Alice do not work the whole task duration. Note - the project is fresh, no calendars are used, no special cases.
If anyone can help me to understand, what's going on, I will be very grateful. I'm stuck with a large project where I'm unable to change resource availability and getting correct results.