When decompressing the Standalone version of Confluence an error message is printed at the end of decompression like this:
tar: A lone zero block at 145270

The decompressed result seems to work without problems though. This warning is apparently caused by different versions of tar having different end of file indicators. I can't find a definitive link on the topic, but http://www-1.ibm.com/support/docview.wss?ratlid=cctocbody&rs=984&uid=swg21270445 is okay.

It's odd that this should start happening in our releases suddenly though.