When using the adjustment brush it will suddenly shoot off a ray of adjustment. For instance here I was coloring the dogs face when an adjustment ray just shot out at 10 0'clock which you can see here in red. It does not seem to make a difference in how feathering is set. I do not have this issue when using a mouse. Do you think I have a defective tablet? Wacom tells me it is an issue with lightroom. (Lightroom 5, Mac OS Yoseminite)
8.4 is a relatively big brush. Are you sure that it does not exceed in size the face of the dog? If so, it is possible that LR has picked a similar colour were it created what you refer to as the 10 o'clock ray. To eliminate this as a possible cause I would reduce the size of the brush.