There seems to be a similar issue with the Eraser for some people. Amusingly enough I've experienced no issues with that, but the Dropper tool lags slightly when switching to it, and then lags significantly when switching away from it to a brush. The issue is absent in Painter X3 on the same machine. Any suggestions for a fix?
I haven't found a fix but I've discovered this IS an issue on my machine.
Switching to the dropper is instantaneous but there's a lag of two or three seconds switching back to the brush. This is even with a basic brush.