Dependent dropdown slicer leaves stale selected elements in place.

I've got a .pbix with multiple (4) drop down slicers at the top of the page...

I've edited the interactivity so that they should be dependent from left to right.  In other words... if you select an element in Resort, it should update the available elements in Season, Purchase Date, and Passes.  Updating the selection in Purchase Date should only affect the elements in Passes.  This is how I'd expect it to work anyway.

What I'm seeing instead, for example, is that if there are elements already selected in Purchase Date, changing the Season will add the appropriate elements, but won't de-select the newly invalid values!

Here's a step by step.  First, select 2017/18 from Season, and legitimate values show up in Purchase Date.  I'll select a few Purchase Dates (okay, fine, months) at this point...

So far, so good.

Now, when I select a different Season, the elements in Purchase Date that I originally selected (which aren't even valid anymore), are still selected!

Why wouldn't Power BI remove these selected elements?!?!?

Since the selected elements aren't even valid, all of my visuals go blank.  Instead, if my Purchase Date just had none selected, the visuals would act like they were all selected, which is more desireable.

How do I get my slicers to interact more... rigidly?  This is a big QA issue.  We can't let users walk themselves into undefined states.

Here's the model.

Thank you community!