I use this widget quite a lot and have never had this problem before or heard anything from our customers about data being shown that was suppose to be hidden.
Are you sure that your MF works 100% of the time? No exception where it might end up in the wrong flow? Easy way to check is to create an easy MF that can only end up one way and test it like 10/15x. If it indeed goes wrong then maybe there is an issue for your Mendix version and the widget.
I’ve also used this widget many times and have not had any problems so far. If you are 100% sure that the MF is working correctly may be there is an issue with your CSS?