Superseding one slicer with another

I have a measure that allows total retail sales (POS) to be displayed by one of four predefined time ranges selected from a “Period” slicer: last week, last four weeks, year-to-date and full year.  In order to make this work, I have a measure, “Selected”, in a “Weeks” table.  The weeks table has a column for each of the first three predefined time periods (“full year” just returns all weeks) containing a True/False for each week if it falls within that time period: Last Week, Last 4 Weeks and YTD.  Here are the two measures at play:

Selected = SWITCH(TRUE(),

   OR(NOT(HASONEFILTER(Periods[Period])),VALUES(Periods[Period])="Full Year"),TRUE(),

        VALUES(Periods[Period])="YTD", CALCULATE(LASTNONBLANK(Weeks[YTD],0)),

        VALUES(Periods[Period])="Last 4 Weeks", CALCULATE(LASTNONBLANK(Weeks[L4],0)),

        VALUES(Periods[Period])="Last Week", CALCULATE(LASTNONBLANK(Weeks[LW],0)))

POS Dollars = CALCULATE(sum([POS_Dollars]),Filter(POS,Weeks[Selected]))

All of this works great.  Now I’ve been requested to add a separate  “Week” slicer that would supercede the “Period” slicer.  In other words, if Last 4 Weeks is selected in “Period” and that’s yeilding weeks 7-10; if a user wants to see just week 5, I want the user to be able to just select that week in the “Week” slicer without clearing the “Period” slicer (to avoid the two slicers containing mutually exclusive time periods).  To do that, I tried modifying the Selected measure to check for a filtered condition on the Week:

Selected = SWITCH(TRUE(),

   ISFILTERED(Weeks[Week]),TRUE(),

   OR(NOT(HASONEFILTER(Periods[Period])),VALUES(Periods[Period])="Full Year"),TRUE(),

        VALUES(Periods[Period])="YTD", CALCULATE(LASTNONBLANK(Weeks[YTD],0)),

        VALUES(Periods[Period])="Last 4 Weeks", CALCULATE(LASTNONBLANK(Weeks[L4],0)),

        VALUES(Periods[Period])="Last Week", CALCULATE(LASTNONBLANK(Weeks[LW],0)))

However, that change causes the “Periods” slicer to be ignored, yielding always the total of all POS unless a Week or several weeks are selected in the “Weeks” slicer.  This is puzzling to me because the Selected measure seems to be working as expected.  Here are some results in a simple matrix (“Weeks” unfiltered):

With original Selected measure:

With modified Selected measure:

Note the Selected measure is giving the same results, but the POS Dollars measure – which filters using the Selected measure – is not.  I’ve tried various ways of including that test for filtering on the Week in the Selected measure – always with the same result.  What am I doing wrong?