MonthToDate formula

[dkc]

Crystal Reports v9.0
I have the following formula
IF {SO_Master.ORDDTE_27} in MonthToDate THEN {@EXTPRICE} ELSE 0
It returns nothing, even though there is data that falls in this range. The LastYearMTD formula also returns nothing, when in fact there is data in this range.
I have a formula
IF {SO_Master.ORDDTE_27} in LastFullMonth THEN {@EXTPRICE} ELSE 0
This formula works just fine.
I can extract the current month to date data with the formula
if {SO_Master.ORDDTE_27} in date(year(currentdate-1), month(currentdate-1),1) to currentdate-1
then {SO_Detail.PRICE_28} else 0

Is there a bug or something in the MonthtoDate or LastYearMTD functions that cause them not to work or what?

Thanks Deb