Filtering on linked date column only keeps timestamps at midnight

Hello,

I have a telemetry data table called telemetry_augmented, with timestamps (millisecond precision), values and metadata.

From the timestamp column, dp_timestamp, I made a Date-version called dp_timestamp_Date. 

dp_timestamp_Date = telemetry_augmented[dp_timestamp]

I made the Data type 'Date' (not Date/time!).

I have a Date table made with this DAX:

Date = ADDCOLUMNS (
 CALENDAR (DATE(2020,1,1), DATE(YEAR(NOW()+1),12,31)),
 "Date As Integer", FORMAT ( [Date], "YYYYMMDD" ),
 "Year", YEAR ( [Date] ),
 "Month Number", FORMAT ( [Date], "MM" ),
 "Year Month Number", FORMAT ( [Date], "YYYY/MM" ),
 "Year Month Short", FORMAT ( [Date], "YYYY/mmm" ),
 "Month Name Short", FORMAT ( [Date], "mmm" ),
 "Month Name Long", FORMAT ( [Date], "mmmm" ),
 "Day Of Week Number", WEEKDAY ( [Date],2 ),
 "Day Of Week", FORMAT ( [Date], "dddd" ),
 "Day Of Week Short", FORMAT ( [Date], "ddd" ),
 "Quarter", "Q" & FORMAT ( [Date], "Q" ),
 "Year Quarter", FORMAT ( [Date], "YYYY" ) & "/Q" & FORMAT ( [Date], "Q" ))

The 'Date' column again is from Data type 'Date'.

There is a relationship between  these two Date columns:

Now, I want to filter data based on the Date[Date] column, which kinda works, but I now only get the points with timestamp 00:00 (midnight). This seems strange to me since the types are not Date/time. 

The reason I am not filtering directly with the telemetry_augmented table columns is because this is a very big DirectQuery table (to Databricks), and the slicer queries the min(dp_timestamp) and max(dp_timestamp), which takes forever. Filtering on the Date table is faster, but doesn't work correctly as described above.

Thanks in advance for the help.