Part of desktop window changed black on flipped portrait display mode

Copied from VSO ID: 23948395

Steps to repro:
- 1. Prepare 19H1 system.
- 2. Execute WPF application. (Please refer to attached ResizeIssue.exe. It is almost empty WPF application made for repro.)
- 3. Press Window key + Left arrow key together for letting the application fit to half of desktop window.
- 4. Open window Settings > System > Display > Display orientation.
- 5. Select Portrait (flipped) mode from combo box.

Expected results:
- Application is displayed as fitted to half of the desktop window

Actual results:
- Part of the desktop window changed black, and the application is displayed as smaller than half of desktop window.
Please refer to attached "Actual_result.png" file.