Unexpected behavior Sameperiodlastyear

Hi,

I'm using the function sameperiodlastyear in some measures and they work fine for all periods besides the current month. I would expect to see the MTD value of lastyear's data there but it shows the full month's value.

Some information:

- I have a dedicated date table with continuous dates created up until today's date

- I have slicers for business year and business month

- I have tried adding a slicer for days. When I select the number of days up until yesterday's date it gives me the correct values in the matrix (both this year and lastyear) but as soon as I select all days MTD, lastyear's values jump to the total month value.

I don't understand why this is happening. Here are my measures and an example of the jump in value:

Total Volume = calculate(sum('Eod brokerspread'[volume]))

 

Total Volume LY = CALCULATE([Total Volume],SAMEPERIODLASTYEAR('Date'[Date]))

 

19th of April not included:

gives this result:

 

19th included gives this result:

 

Total Volume LY above is the total of April last year's value and not between the 1st and the 19th.

 

Can someone explain why it treats sameperiodlastyear as a full month as soon as all dates month-to-date are included?

Btw i've tried changing sameperiodlastyear with the following formula with exactly the same result.

Total Volume LY = CALCULATE(sum('Eod brokerspread'[volume]),DATESMTD(dateadd('Date'[Date],-1,year)))

Also read this blogpost already where it explains that sameperiodlastyear and the above logic are the same:

http://mdxdax.blogspot.com/2011/01/dax-time-intelligence-functions.html

Thanks,

Chris