For default.lgf sign conversion formula is:
SignedData_Result = if(Result.ACCTYPE=INC,LEQ, -1, 1) * Function(if(Argument1.ACCTYPE=INC,LEQ, -1, 1) * SignedData_Argument1, if(Argument2.ACCTYPE=INC,LEQ, -1, 1) * SignedData_Argument2, ...)
((-100*-1+1000)/100)*-1 = -11
In the report INC accounts are shown with sign reverse: (-11)*-1=11 in your case
DM package script in BPC 10 don't perform any sign conversion:
(-100+1000)/100 = 9
In the report INC accounts are shown with sign reverse: (9)*-1=-9 in your case
Vadim
P.S. In general it means that you can't use the same script as a default.lgf and in DM package!