See the image.
I can't figure out how I have done this, but my source folders appear like this, rather than in a hierarchy. When I open the folders in explorer, they are all nested as you would expect, folders inside folders. They are not folders with / in their name.
This only occurs in this one specific src folder of this one specific project. So, I feel like it's a configuration specific to this folder. I've even tried closing the entire project and adding it again.
Anyone seen this? I don't even know what to search for... I think it might be an inherited eclipse issue, rather than a specific thing about STMIDE.
