I recently encountered a .tar file which DICE tar wouldn’t extract, giving multiple warnings:
tar: Ignoring unknown extended header keyword `SCHILY.[...]'
before bailing out due to previous “errors”. The file in question appeared to have been created on a Mac, whose archive utility adds extended metadata to its files.
This is confirmed and fixed in May 2007, but some more venerable Linux distributions continue to ship older versions. Tar’s behaviour is a bug, since these warnings should be non-fatal. However, the warnings can be avoided altogether by addition of an argument:
for each problematic keyword.
[Source: Tar mailing list]