Pivot control becomes a focus trap when a keyboard accelerator causes a child listview to be cleared

[danbelcher-MSFT]

Describe the bug
This bug is very specific. Given a PivotItem containing a ListView with items and a Button that clears the list, the Pivot becomes a focus trap if the Button has focus and is invoked by keyboard accelerator.
Visual tree shows focus is stuck on the Pivot's HeaderClipper element.

Steps to reproduce the bug
Sample app is available here: https://github.com/danbelcher-MSFT/PivotFocusTrapRepro
The specific changes I made for this to repro can be found in this commit: danbelcher-MSFT/PivotFocusTrapRepro@621fa71

To repro, add a few items to the list, navigate to the Delete button, and press Ctrl+L to invoke. Navigate to the Pivot header and observe that focus is trapped.

The bug only seems to repro if the button is invoked by keyboard accelerator. If invoked with mouse/space, the bug does not repro.

Expected behavior
Pivot should not become a focus trap. Behavior should not be different if the Button is invoked with keyboard accelerator vs other methods.

Version Info

Bug repros in XAML framework.

NuGet package version:
Bug also repros in Windows Calculator's History/Memory list.
[Microsoft.UI.Xaml 2.1.190405004.2]

Windows 10 version	Saw the problem?
Insider Build (xxxxx)	18890.rs_apps.190427

Device form factor	Saw the problem?
Desktop	Yes

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