When using the pen tablet’s pen pressure sensitivity, the location of the previous color may change.
Aseprite version is v1.3.2-x64, OS is Windows10
Settings are Pressure/Size checked, Pen size is 5, and Pixel-perfect is Off.
When you draw a line on the screen in this state, when you draw the next line or press the Alt key, the location and thickness of the previous line may change and become corrupted.
It seems that there is probably a discrepancy between the data displayed on the screen and the data handled internally, and it changes when the screen is refreshed for some reason.