Images can be uploaded in the form 123px-Something.jpg. This clashes with the
new structure of the thumbnail directory in 1.5. If a thumbnail of
123px-Something.jpg is requested, the script attempts to create a directory
called 123px-Something.jpg, but that name may already be taken by an actual
thumbnail image left after 1.4 conversion. Thus, warnings and broken thumbnail
links are issued on render.