I believe this stems from the behavior where AjaxFS creates a blank folder first. It appears as a textfield in the tree, when you enter a new folder name, it does a rename of the folder from "New Folder".
I think the name defaults to
"file-storage-new-folder-$unique_id"
I hate to answer a question with a question or two BUT ...
In regular file storage with no AjaxFS, if you create a folder and then rename that folder, does fs::get_folder still work ? Where and how are you using fs::get_folder ?
On the AjaxFS side, we could fix this by asking the user for the foldername before creating a folder instead of the current behavior.
However, before I attempt the fix I would like to know how you and other devs are using fs:get_folder and the other fs api where you pass the name as a parameter specially after a folder or file has been renamed.