WinForms app using WindowsXamlHost crashes when focus is changed away and back to the app

[nmetulev]

Re: #2456

I'm submitting a...

• Bug report (I searched for similar issues and did not find one)

Current behavior

Create a new Forms app, add the WindowsXamlHost with UWP content and launch app. Change focus away from app and back to the app. App crashes

Expected behavior

App should not crash

Environment

Nuget Package(s): Microsoft.Toolkit.Forms.UI.XamlHost

Package Version(s): 

Windows 10 Build Number:
- [ ] Creators Update (15063)
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [x] Insider Build (build number: 17758)

App min and target version:
- [ ] Creators Update (15063)
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [x] Insider Build (17758)

Device form factor:
- [x] Desktop
- [ ] Mobile
- [ ] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio 
- [x] 2017 (version: )
- [ ] 2017 Preview (version: )

ping @ryalanms

[rjmurillo]

Isn't this fixed with #2497?

[rjmurillo]

Ryland checked and #2497 and #2502 should put the WinForms stuff in a relatively good place (still some weirdness with focus and activation, but that will get fixed in future Insiders OS updates and we can remove the focus workaround).