DropShadowPanel not applying properly to rounded grid.

[ghost]

Describe the bug

DropShadowPanel not applying shadow/masking properly on grids with CornerRadius.

Steps to Reproduce

<controls:DropShadowPanel BlurRadius="3" Color="Black"  IsMasked="True">
      <Grid CornerRadius = "30"/>
<controls:DropShadowPanel/>

Expected behavior

The shadow should be rounded to match the rounded grid.

Screenshots

Environment

NuGet Package(s):

Package Version(s):

Windows 10 Build Number:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [ ] May 2019 Update (18362)
- [x ] May 2020 Update (19041)
- [ ] Insider Build (build number: )

App min and target version:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [x ] May 2019 Update (18362)
- [x ] May 2020 Update (19041)
- [ ] Insider Build (xxxxx)

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

Visual Studio
- [ ] 2017 (version: )
- [ ] 2019 (version: )
- [x ] 2019 Preview (version: 16.10.0 preview 3.0)

Additional context

[ghost]

Hello dollscythe, thank you for opening an issue with us!

I have automatically added a "needs triage" label to help get things started. Our team will analyze and investigate the issue, and escalate it to the relevant team if possible. Other community members may also look into the issue and provide feedback 🙌

[michael-hawker]

This is a known issue, see #3516 and #3607.