When reporting problems with modules, report version numbers, use Devel::Modlist like

$ perl -d:Modlist -e "use CGI;"
CGI                    3.51
CGI::Util              3.51
Carp                   1.11
Exporter               5.63
constant               1.19
overload               1.07
vars                   1.01
warnings               1.06
warnings::register     1.01
[download]

Now, looking at the source of Archive::Tar::Streamed, there is literally nothing to it, its barely 45 lines, and it hasn't been updated since 2005, while Archive::Tar has on 18 Dec 2010.

I would ask the Archive::Tar maintainer to review Archive::Tar::Streamed, he should be able to tell instantly if syswrite $self->{file}, $tf, length($tf) - (BLOCK * 2); makes sense :)