Connecting two tables with dates

Hi,

I have some doubts with relationship through dates.

My aim is to have a single table called "Calendar" where I connect all the DataTable with dates, so use only the date into "Calendar" to works with time across the report.

I have 2 cases in the screenshot, both the table "Calendar" and "Calendar 2" have the same data set. 

"Calendar", and so "Calendar 2", is a LUT table having only the function to generate a calendar from 2018 to date. In this sense in these two table there are no repeting dates.

In "Sales" there are dates from Jan/21 to date and for every day the corresponfding value of Qty and Value sold. Every dates is unique except to 08/01/2021 (DD/MM/YYY) that is repeated 2 times.

In "Sales 2" there are dates from Jan/21 to date and for every day the corresponfding value of Qty and Value sold. Every dates is unique.

Recaping the only difference between the two cases in term of data is a single row into Sales that is repeted 1 time.

Now the questions:

1. why in the report once I connect the filed "Data" (Date in Italian) the Hierarchy in the case 1 fo "Sales" is cancelled?
2. why in the case 2 I cannot chooose the direction of relationship?
3. why in case two if I drag Data from "Sale Unic" to "Calendar 2" the Hierarchy in Data of "Sales Unic" is cancelled? And if I do the opposite, so drag Data from  "Calendar 2" to "Sale Unic" the Hierarchy in Data of "Calendar 2" is cancelled? Even if the arrow of relationshiop is the same?