"ContentPresenter.Content" memory leak

Question

I'm working with the following: VS 2010, .Net 4, WPF and the .Net Memory Profiler version 4.6.40.0 Pro. They're all running on Win7 64-bit. I've been using the .Net Memory Profiler to track down memory leaks and found one that I don't understand even though I appear to have fixed it. We have a control that contains three ContentPresenter objects. If I set the Content property of the ContentPresenter objects to null in our Cleanup method then the control doesn't leak at all. If I don't null out the Content properties we get a large leak (about 3.5 MB each test).

The results that I saw in Google searches didn't appear to address this issue directly. The documentation for ContentPresenter didn't help me either. Does anyone here understand why nulling Content fixed the leak? Is there a better way to accomplish the same thing?

I will note that one of the ContentPresenter's is dynamically switched between a WindowsFormsHost and a BitmapSource to handle airspace issues.

Update: here are the relevant parts of the cleanup:

First, null out the ContentPresenter's

AddressGridPlaceholder.Content = null;
AddressFormPlaceholder.Content = null;
MapControlPlaceholder.Content = null;

Then clean up the WindowsFormsHost

if (_hoster != null)
{
    _hoster.Child = null; // Remove the map control reference first
    _hoster.Dispose();    // Then Dispose
}

Answer 1

Why does it seem to mee that you are not using control binding.It's not great to play with this things, manually.