I am also facing a somewhat similar issue. I have checked the old discussion in above post and added the changes, but it is not working for me.
I have a property with BASETYPE as NUMBER in custom widget, for which I have set "isBindingTarget" as TRUE and default Value of 15. In the Mashup Composer I am passing a value from service to this widget property, This value from the service is 30.
When I am loading the mashup, I see that the widget is taking value of 15 instead of 30 when I am calling "this.getProperty()" to read the property value.
As suggested in the URL discussion of previous post, I also added the updateProperty block of code. Also my value is not changing continuously. But the value for any property must be taken from the binding if any binding is present.