@IlyaIvanovArt - undo is disabled by default. It significantly improves painting in the viewport across all hardware configurations. We let the end-user decide if they want to enable it or not. :smile:
If you enable the wireframe, does it still happen? If it shows fine with wireframe, I have the same bug, but usually just using a mental ray shader fixes it.
uncheck any boxes in the transform constraints marking menu Looks like you have edge slide enabled. resetting the tool should take care of that though.
You should make all channels black with a white dot (just pass of a brush, not a single a pixel). Using all white means it will have everything enabled.
Can you post the guide you are using? Maybe try enabling the the global supersampler in the Render Setup | Renderer tab. And change the Antialiasing filter to Catmull-Rom.