While weight painting armatures on the face of a character, I shift back and forth from bone to bone. I am having two strange problems with one more strange than the other.
The first problem is that if I had, for example, painted the entire head of the character for the head bone and then shifted to a lip bone and painted it then shifted back to the head bone, the part of the lip I painted would be unpainted.
The other problem I'm having is stranger. When I select face bones, random portions of the face have been painted by what I presume to be auto weighting. When I use subtraction to deselect those areas everything works, however, if I do more subtraction for other bones and then go back to a previous one, there is more random weight painting linked to it in a place I never painted before so I can never paint any bones without them being effected by this unintentional "ghost painting."