Clarity

We have tasks with assignment for each task one resource.

example task QS2

Task 13.1. - 24.1.

Assigned ressource with ETC 20

We made timesheet for 20 - 23.1 -  6 hours for every day 24 i total

Approved timesheet and job "post timesheets" started.

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Task start and finish dates changed:

start 20 finish 23 - like there are timesheeted.

In previous versions was changed only ressource assignment start and finish dates not task start and finish date.

Has anybody idea how to prevent this?

You can't prevent this as far as I know.  Standard behaviour at posting is that the task start date will change to be the date that assignment actuals are first booked. Task finish will also be set to the latest assignment end date (this will include ETC, but in your example as you have used up all the 20 hours ETC by posting 24 actuals, it's the latest actual date that is used).   As you only have one resource assigned, their assignment start and end date will always match the task start/end date.

Thanx for confirm I though its that way :).

Vit