Windows 10 (64 bit)
Short description of error
Saving a new file / directory with spaces in the file name will cause the entire path to be recreated with underscores. This only appears to happen with new content containing spaces,
Exact steps for others to reproduce the error
File > Save As
Existing directory: "C:\Users\test\Desktop\Graphic Work\Blender\"
New folder: "Halloween 2015"
New file name: "Halloween 2015.blend"
Upon save, the UI will briefly display an error message along the lines of "given path is OS-invalid" before saving.
Final save path: "C:\Users\test\Desktop\Graphic_Work\Blender\Halloween_2015\Halloween_2015.blend"