Unicode strings need to be converted to UTF-8-encoded bytestrings before they are handed off to "add_data()":

##</code><code>##

-    $tar->add_data($filename, $serialized_context, { type => Archive::Tar::FILE });
+    $tar->add_data($filename, encode_utf8($serialized_context), { type => Archive::Tar::FILE });

##</code><code>##

-    $self->serialized_blob($serialized_context);
+    $self->serialized_blob(decode_utf8($serialized_context));