Currently, (AFAIK) the selection nodes select type (Vertex, Edge, Face) depends on what you selected in the viewport when you press Set Preview.

This has a couple problems:

1. It is not intuitive to switch the selection type on selection nodes. (you have to press set preview, change the selection mode in the viewport, then set preview something else)
2. The selection type is not tied to the node, so you can't see what selection type a node has currently.
3. You have to remember what selection type each selection node has, since when you press set preview on selection nodes, you have to make sure to switch the selection type in the viewport to that node, otherwise break your entire model.

This also means that just by pressing Set Preview on selection nodes, you can change what your model looks like in the end, which probably should not be what the button does.

I propose to have the selection type attached to each selection node instead, so that the node looks like this:

I have most of the skeleton coded up already (here), so if you think this is a good idea, I'll go implement it in the rest of the applicable selection nodes.