Link value in nested grid is lost on insert

Hi
I have grid Parent with his form → working when used alone
I have grid Child with his form → working when used alone

I created a nested grid - advanced, so that I can add also records in child.
The display is OK, the information is properly presented.

The link field Parent->Child is not displayed in Child grid. But it is in the table and is configured to go to Child Form as parameter. All is OK
When I try to insert a record in Child, that field does not have the correct value and the form inserts random values into the table. It seems the parameters are lost.

Anybody encountered similar situation?

Look here for the full situation: https://www.youtube.com/watch?v=l_PNe4LzNeo