Weird behavior after creating relationship

I think this article explains what you are seeing.

Mark as Date table - SQLBI

Here is the relevant snippet

In order to simplify the usage of time intelligence functions, the DAX engine makes an assumption when two tables are related through a column of Date data type: When a filter is applied on the key of the relationship – Date[Date] in this example – the new filter overrides any other filter on the Date table. It basically applies a REMOVEFILTERS ( Date ) to the filter context every time you apply a filter on the Date[Date] column. This behavior occurs automatically only when the relationship is based on a column of Date data type.

You can obtain the same behavior – that is, adding REMOVEFILTERS on the table whenever a new filter is applied on the Date column – by marking the table as a date table. When you mark a table as a date table, Power BI asks which column contains the dates of the calendar. This is required because the engine adds REMOVEFILTERS every time you apply a filter on that specific column.

Regards,

Pat

Hey,

late to the party, but nevertheless I want to share the link to one of my favorite DAX articles. This one has been written by Jeffrey Wang some time ago:

MDX and DAX topics: DAX Time Intelligence Functions (mdxdax.blogspot.com)

As mahoneypat already mentioned the behavior is related to the internal workings of related date columns. Here is the relevant snippet from this article:

If a Calculate filter has a unique column that is of data type date/time, all previous filters on all columns from the table which contains this date/time column are removed.

 I still read this article, whenever I'm facing some more complex DAX challenges where the calendar plays its part, sometimes in preparation, but most of the time to fix things 🙂

Regards,

Tom