Issue

Attempting to append or concatenate to a compressed tar should not work, but attempts to do so produce core dumps with a SIGABRT signal rather than print an error message..

This can be reproduced with the following:

  # echo hello > junk  
  # echo goodby > junk2  
  # tar zcf junk.tgz junk  
  # tar zrf junk.tgz junk2

Replacing the "r" option with "A" produces the same results.

Using j (for bzip2 compression) rather than z (for gzip compression) also aborts.

This behaviour is (somewhat) expected.

You would not be able to append to a compressed archive according to the documentation.

"info tar", section 8.2.1 has some verbage to that effect...

<snip>  
   Notice also, that there are several restrictions on operations on  
compressed archives. First of all, compressed archives cannot be  
modified, i.e. you cannot update (\`--update' (\`-u')) them or delete  
(`--delete') members from them. Likewise, you cannot append another  
\`tar' archive to a compressed archive using \`--append' (`-r')).  
Secondly, multi-volume archives cannot be compressed.  
</snip>

See  Bugzilla #675693 for more details