E
ejo
I happen to have the very same model and Windows 8.1 so I can confirm this.
Interesting thing is, that if you quickly double tap and start to draw with second tap, it works fine.
But because it occurs not only with drawing but also any input (sliders etc.), it doesn't seem like programming error. I also tried an random AIR app I found from internet and this happens with it also, so this bug is between AIR and Wacom drivers. I haven't used portable version and don't know how different it is than AIR version (technically).
I don't have time to investigate this any further today, but I'll report if I found something later.
