I have an entity called 'SelectedMonths', which contains a list of 'Month'.
What I am doing wrong?
If you add the 'NewMonth' to 'MonthList', then why a second retrieve, you'll be able to use this 'MonthList' with the newly added month immediately.
Also, I would try to avoid using plural names for entities.
Is the 'MonthList_2' an database retrive? Did you commit the object: 'NewMonth'?