weird shapes in the sculpting with multires

Support Modeling
1

Every time that I change the subdivision of a model that i have the mesh corrupts some vertex and make strange shape like this


Why happens this? blender have some solution to this bug? is really boring see new problems every time that I move between subdivision levels.

2

I also have this problem with my multires. As far as I can figure, just attack it with the smooth function. But otherwise I don’t honestly know.