When using the Wacom pen that came with my Lenovo Ultrabook, some problems occur using the freehand brush tool. Sometimes, the line is very offset while only on the canvas, but still has varying weights. Then, when I restart my app, the line is perfectly oriented, but there is no pressure variation.
I'm sorry, but you'll have to report problems like these to wacom. It's their driver that's the culprit. If you don't get pressure support after restarting krita, that's because the wacom driver doesn't give krita a context; if you get offsets before restarting it's because the driver gives krita bogus tablet events. And before you say, but app X -- that's not so relevant, these drivers keep state for each application and that means they might give different input to different applications. When this happened to me with my wacom mobilestudio pro, I had to reset the driver settings completely.