I can’t reproduce the issue on my machine (Windows 10) and a virtual machine (Windows 7), but it might be related to graphic driver. Which version of OS and graphic card are you using? Can you try updating the graphic driver?
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.