I can reproduce the issue with Win7 64bit and Emed64 v17.7.92(or later) ~ v19.
1. Open a 100 lines text file with maximum window.
2. Enable DirectWrite.
3. Press Ctrl+Alt+Del and then press ESC to switch back.
4. Use mouse wheel to scroll down, you will see the “black” block.
Emed64 v17.7.91 or earlier is OK.