I added the first version of multi-bone selection for faster, temporary locking/unlocking; right now, if multiple bones are selected, the selection is considered unlocked, despite any vgroup checkbox status.
Every other group is considered locked.
paint_vertex.c
A modified Auto Normalize was inserted to normalize the active group normally instead of locking the values: it was causing the active group to steal weights from locked groups if the active group had a weight of 1.0, and that destroyed the locked groups deformations.