Some screen dirt after pressing [1:1] button

Sometimes, pressing the [1:1] button, i see some dirt near this button. It seems not to happen if the aseprite window is relatiely small ( 800x600) and it happens for shure running aseprite fullscreen on my 1920x1080 monitor.

(Aseprite 1.2.3 on Windows7)

Thank you.

Known issue:

Never got some time to finally fix this one.