Bug 367613

I was trying out making custom brushes and testing them out on the testing area. 
While doing so I accidentally pressed the buttons that are on the tablet pen. These buttons are bound with Right- and Middle Click respectively. While holding either of the pen buttons down and simultaneously pressing the pen tip onto the tablet surface to draw, Krita won't draw anything onto the testing area, and won't do so until the software has been restarted. 

This means I have to restart Krita in order to try the brushes I'm customising, at least on the testing in the brush editor.

Reproducible: Always

Steps to Reproduce:
1. Bind tablet pen button(s) with either Right- or Middle Click
2. In Krita, open "Edit brush settings"
3. While drawing onto the testing area, hold down the tablet pen button


Actual Results:  
I'm now unable to draw onto the "area" until Krita has been restarted.

Expected Results:  
Krita should've been drawing onto the testing area.

OS version: Windows 7 Ultimate SP1, 64-bit

Tablet model: Wacom Intuos5 Medium
Pen model: Wacom Pro Pen
Driver version: 6.3.6-3