Why can't my mat checkbox update the correct value?

in my app I'm using a BehaviourSubject which I toggle value to update a MatCheckbox. only problem is that the value doesn't get updated to the correct value, in this StackBlitz the value of isChecked is supposed to get setted to false each time I check the checkbox but the value don't get updated.

I've been looking over internet without seeing an answer to my case