This is a note on the bug/mysterious phenomenon encountered on Windows where pressing the shift key in text editors like Atom and Notepad causes downward scrolling.
To get straight to the conclusion, it was fixed by restarting Windows.
Such problems are often solved by restarting Windows. However, if it doesn’t fix with a restart, you might want to check Stack Overflow or similar resources.
Alternatively, performing a Windows update might fix it. However, since updates take time, it’s good to try a restart first, and if it doesn’t fix, then perform an update.