While the mouse button is down when resizing the main Aseprite window, the window redraws itself by simply scaling the window to the new size. When the mouse button is released, the window redraws properly. The window should redraw itself properly continuously while the mouse button is down. Other Aseprite windows like Preview, Preferences, About already do redraw themselves properly while resizing (though it's questionable whether most of them even need to be resizable).

Aseprite and System version

• Aseprite version: 1.2.25 built from source
• System: macOS 10.13.6