Why Assignee returns bad values?

Hi, I have such a report:

Time → Select individual members → All times.

Assignee → All hieratchy level members → User
Issue → All hierarchy level members → Issue

Measures → Predefined → Hours spent
Measures → Predefined → Issue properties → Issue assignee

and I get this screen.

When I go inside RBD-3060 task (the first one), I see that this task was created by Lukas, Dawid is assigned to that task and only Dawid have logged hours for this task.

There is also NO Andrzej in the whole history of this task.

How can I prepare trustworthy reports per Assignee if Assignee dimension returns bad values?