There is something awry with the viewport navigation/ camera zoom/ camera translate in Painter 2018.
I'm using a Wacom Intuos 4 tablet, with camera translate mapped to 'ALT + middle-click' and camera zoom mapped to 'ALT + right-click' in Painter.
When I actually try to navigate in the viewport, this is messed up somehow. 'ALT + middle-click' zooms the camera view instead, and 'ALT + right-click' translates the camera.
This is very, very annoying.