keyboard input sometimes broken when multiple instances open

Describe the bug
If you have more than one instance of Calculator open, which ever instance is not the "original" will lose certain keyboard functions.

For example pressing escape to clear, backspace to backspace and enter to sum. These keyboard keys no longer work on the second instance. I cannot reproduce this 100% of the time. But every time I have encountered this problem, it was when multiple instances were opened. And

Steps To Reproduce

1. Open calculator
2. Hold shift and lose focus of the window (easiest way to do this is just to hold shift and left click somewhere outside the window)
3. Regain focus of the window
4. Press keys such as enter backspace escape p l x y and probably more

Expected behavior
Keyboard input should be observed no matter how many instances of calculator are open.

Device and Application Information

• OS Build: 10 0 17134 0"
• Architecture: X64
• Application Version: 10.1903.21.0
• Region: en-US
• Dev Version Installed: False

Note: A team member edited this comment to clarify steps to reproduce.

No source file or test is named. Start by reproducing the listed focus-change sequence with multiple Calculator instances, then trace the application's keyboard-input handling. Done means Enter, Backspace, Escape, P, L, and X/Y continue to work after focus is lost and regained, regardless of the number of instances.