This issue happens on screen areas that have "application with transparency," like when the magnifier tool is open.
Steps to reproduce:
- Join a meeting.
- Open an onscreen tool like Magnifier (which has transparency) and place it where the palette opens up.
- Open a PowerPoint presentation.
- Start application share of PowerPoint.
A black box appears at the lower-right corner (where we placed the Magnifier). If it is an application/window sharing, then that area is seen as hatched.