Simple scene, nothing out of the ordinary, except when I painted the first brush stroke I got this warnings dialogue. I've never seen it before and I can't seem to reproduce it again. Odd.
The painted shader appears to be doing its job correctly, though. ???
Screenshot attached...
That looks like a one time error, a little bug that made the program skip a command line or something...
It missed the 'Start brush stroke' once, so the program got confused and put out a warning.
Next stroke was alright, telling the program when starting and stopping again.
This is all a guess though.
I got this warning, too. I see it only once while I was working on my last (Image #9) image. But I couldn't find any differences to the normal work of the painted shader.