Hi Konstantine,
The synchronization of the update role tasks can be tricky - the update task holds just the one or few users from the source - when you stage this task, the update means that add the users who are in the task and remove all others"" - this is according to the udpate task data and it is updating the role.
I understand this is causing confusion and issues. This behavior is basically the same for any object with children objects.
Best regards,
Juraj Ondrus