CLOSINGBALANCEMONTH BUG?

in CLOSINGBALANCEMONTH is a BUG??

Like: You have a quantity per day and you want to know the quantity every last day per month

If you use it, it will show the quantity combined with the last date of a month, but when there is no quantity on last date of the month, you dont see a quantity.

there are several measures: Northwind database

QuantitySum = SUM('Order Details'[Quantity])

ClosingMonth1 = CLOSINGBALANCEMONTH([QuantitySum]; tblCalendar [Date])  , date based on linked calendar

ClosingMonth2 = CLOSINGBALANCEMONTH([QuantitySum]; Orders[OrderDate]), date based on orderdate

ClosingEOM = CALCULATE ( [QuantitySum];ENDOFMONTH ( tblCalendar[Date] ) )

in july 1996 there is a quantity on the last date of july, so it works

on august 1996  there is no quantity on last date of august, it does not work (combined with date calendar)

see pictures

july, with result

 august, no result

but only based on order date will show the last date which is used (not the last date of a month

ANYONE, IS THIS A BUG??