tl;dr: Medium users typing in Polish couldn't enter the letter Ś because the editor blocked Ctrl+S to prevent the browser's save dialog. The bug arose because Polish keyboards use Right Alt+S to type Ś, and Windows internally maps Right Alt to Ctrl+Alt—so the editor's Ctrl+S handler was swallowing the keystroke. The fix was a one-line change: only block Ctrl+S when Alt isn't also pressed.