I came across a problem few days back where I was not able to create Folders ending with _files and with the name Forms.
i.e image_files, Research_files
This is by design in SharePoint due to thicket. A thicket is what you get when you save a file as an HTM that contains content such as graphics. To store the additional content, which can not exist in the HTM file, the application creates a linked folder. It names the linked folder, filename_files. When a thicket is created in SharePoint site it is always hidden.
To avoid the confusion of thicket getting mixed with the user created folder SharePoint does not allow the folder to get created and instead replace an underscore after the folder name when creating manually i.e image_files_ . While creating the folder with Object Model it throws an exception
Forms is also a hidden folder in Sharepoint so does not allow to create it at the root level.