duplicated to NIM071688 which has been fixed in 10.1 final
対処法
Import the 1-bit TIFF into the file geodatabase and create a mosaic dataset (do not specify pixel type or number of bands). Add the 8-bit TIFF first (check on Update Overviews), click OK. Add the 1-bit TIFF from the file geodatabase (processing template: stretch, check on Update Overviews) and click OK.