Nodes doubling and changing in Paths

When editing a path very often after I've deselected a path and then selected it again my nodes have changed, the most common is that a single node has been split into two overlapping nodes (small diamond) and something else that keeps happening is that a previously smoothed node (square) becomes a corner node (diamond).

I believe this might have something to do with some sort of validation function that runs over the path after it's been deselected, but I'd really like my path to stay the way I defined it.