Some third party backup products may by default restore CACHE.DAT files as UNIX sparse files when there are trailing zeroes in the backup file.
The support for sparse files vary from UNIX distribution and file system types. Sparse files attempt to use file system space more efficiently when blocks allocated to the file are mostly empty similar to thin-provisioned storage. The file system transparently converts metadata representing empty blocks into "real" blocks filled with zero bytes at runtime. The application is suppose to be unaware of this conversion.