One problem is that the cursor seems to be misaligned when using the Wacom Cintiq tablet. If I use the mouse, everything's right. If I use the tablet in any other app (like Krita), everything's right too. But using the Wacom Cintiq with Paintstorm Studio makes the cursor shifted a little. The same problem seems to appear if I run the Windows version on Linux using Wine, but the Windows version has an additional option in the settings that actually fixes the issue. The Linux version doesn't have that option, unfortunately.
Another problem is that the interface element stretch beyond the window, and it's impossible to make them smaller. It looks like this.
And the elements can't be resized. Even if I make the entire program's window much larger than my screen, and then move it around so that I can see the end of the Layers panel, clicking and dragging on the bottom edge doesn't do anything, even though it's supposed to resize the panel.
