setProperty can't set right value in arm platform when type is qreal

I define a property which have is qreal type,just like this:
Q_PROPERTY( qreal opacity READ opacity WRITE setOpacity )

when i call setProperty to set value, it doesn't work right in arm platform
obj.setProperty( "opacity", QVariant( op ) );
obj.setProperty( "opacity", op );
obj.setProperty( "opacity", 0.2 );
I use qDebug to print the infomation, and the argument is 1.575 ,not 0.2