I've put together two sample apps to demonstrate the same scenario, one in C++/WinRT, the other in C#/WinRT:

C++/WinRT: DesktopWinUICppLeakTest.zip

C#/WinRT: DesktopWinUICSharpLeakTest.zip

In both cases, the app contains a ListView containing 1,000 items, plus a button that navigates to and from a second page also containing a ListView with 1,000 items. In the C++/WinRT case, the memory footprint of the app stays the same after successive navigations, whereas in the C#/WinRT case, the memory footprint steadily grows. A heap dump analysis indicates that the root Page object in native code is what's leaking, so it's likely the case that something in the C#/WinRT projection is holding onto the native object past when it should be.