Hmm. Did you maybe recently upgraded FlowCanvas, but between the upgrade you already had some missing nodes in some of your graphs by any chance?
The serialized fields definetely do contain the underscore (you can confirm this by opening up the MissingNode.cs file for example), but this has recently changed. Thus, the only way I can see this happening is if you upgraded with some Missing Nodes already existing in some of your graphs like stated above.
I would not really recomend making the change you mentioned because it would break the funcionality of finding missing node types and recovering them.
Gavalakis
