I faced similar problems, in my case was a problem with SCIFIO reading the tiff: Differences between using component ITKImageIO and explicitly setting ITKIOTIFF
Do you have Module_SCIFIO on?
When you use the reader without specifying the format, SCIFIO gets picked over ther regular ITKIOTIFF for tiff images. Try setting it manually (see link above) and see if the image dimensions are read properly.