Yes, you can read, but something else gets read *after* the kernel you uploaded (probably the whole space allocated for kernel). If you wish to compare downloaded kernel image with the original, compare only up to the length of the originally uploaded file (as Mark is doing in the script he posted when uploading was not fully reliable). Use

dd if=longer_file bs=length_of_shorter_file count=1 | diff shorter_file - 

under Unix (don't know equivalent on Windows, except with cygwin or MKS toolkit).