Seeing as the error happened on the same place each time, it might sound like you were getting errors that didn't _always_ get caught by the checksum algorithm (i.e the error "happened" to match the checksum) (maybe).
Sounds like another good reason to do separate checksumming of files after download (read: sha1/md5).
Oh yes, crypto checksum is always useful. Another bug (also eons ago) was where something was trying to patch the TCP options, with a very lax assumption about the packet - as a result with some way fragmentation it would think it was patching the option, whereas it was smashing the payload... Of course, after patching the "TCP option" it was adjusting the TCP checksum, or, rather, the place where it thought the TCP checksum was - which in that case was again within the payload.
Needless to say the whole operation made the corruption checksum-neutral from the viewpoint of the "real" checksum - so it was not caught by the TCP checksum, as a result the files were sometimes silently corrupted.
Took a lot of work to catch and debug, the symptom was that Gentoo's packages appeared to be corrupt and failed the SHA1 checksum check.
So, indeed, cryptographic checksumming of files is a good thing.
Seeing as the error happened on the same place each time, it might sound like you were getting errors that didn't _always_ get caught by the checksum algorithm (i.e the error "happened" to match the checksum) (maybe).
Sounds like another good reason to do separate checksumming of files after download (read: sha1/md5).