Subtotal not correct

Attached is my reply, although i dont' understand why you are totaling the 'AmountYTD' values in 2016 to get 1000.  Seems like you would want the subtotal to be 400 for 2016.  

Sample reply

This gives me this strange result (AmountYTD is the original dataset, testQTD is the new result:

I'll continue thinking throught it myself too.

UPDATE:

This is almost there:

testQTD =
var _thisQ = TOTALQTD( [Total Amount], dimDates[DAXDate] )
var _lastQ =  TOTALQTD( [Total Amount] , PREVIOUSQUARTER( dimDates[DAXDate] ), VALUES( dimDates[Year] ) )
RETURN
IF(_thisQ = 0,
        BLANK(),
_thisQ - _lastQ)

Just got to figure out how to total 2017.