I think the creation of an image file, organizing a file system on it and loop-mounting that file system, may be relatively safe on NTFS. But, as NTFS is a rather swiftly and erratically moving object, I can't really understand how anyone can be quite sure everything will always go well. Even if everything works perfectly today, there is a chance that the next service pack, or even bugfix patch, may introduce problems. Therefore, I like to make a distinction between simple tasks like creating, updating and reading an image file, and more general file system use. In particular, if all reading/writing to the image file is to be done under Linux, one may mostly avoid inconsistencies etc between Windows and Linux NTFS implementations.