I have created two very basic test reports to work with to simplify the process
they both use the same table of data
Report 1
Page 1 Is just filtered on year and has a few visuals.
It contains column charts with month on the Axis

Page 2 is a basic table
Drill through field is Month and Cross report is switched on On

Report 2
Page 1 is Filtered on Year and Region and has a few visuals including a column chart with Month on the Axis

Report 2 is the source because we will be drilling through from here
Report 1 is the Target because we are drilling through to page 2 from Report 2
Cross Report Drillthrough Toggle

Cross Report is set to ON for the Source Report (As above)
Leave Cross Report Set to Off for the Target Report
Report Setting Options
Both reports are Set File > Options and Settings > Options > Report Settings
Cross Report Drill through – Allow Visuals in this report to use Drill through Targets from other reports

Both reports are published to a workspace.
Once in the Service I create a very simple dashboard from a visual from each report as my starting point
here is where it goes wrong

Start at the Dashboard and go to region. click on the Total from region report Tile

Once in here I right click and get the drill through on the Other report, So far so good. I click this and go to the drill through

Note that the filters are kept as expected from the region report.
Now I decide to go back to the dashboard because I want to go to the main report.
In this case I click the back button (Because the back button doesnt work on the report when you move between reports)
Or I can simply click on the Bread crumb trail of POC reports and Dashboards and go back to the dashboard this way

This time I want to go to the main report with just the Date slicer.

And this is where the problem lies. Notice that the filters from the drill through are still applied so this year report is filtered by Month and region.
When moving back to the start we don’t want the drill through filter applying. If you drill through in the same report this works absolutely fine. You can go back and the filters are unapplied. However they arent unapplied when drilling through to other reports.
The Solution
For each report if you go into File > Options and Settings > Options > Report settings and make sure Persistent Filters is ticked ‘Dont allow end users to save filters’
