http://stackoverflow.com/questions/1964806/short-read-from-filesystem-when-can-it-happen

Disk-based filesystems generally use uninterruptible reads, which means that the read operation generally cannot be interrupted by a signal. Network-based filesystems sometimes use interruptible reads, which can return partial data or no data. (In the case of NFS this is configurable using the intr mount option.) They sometimes also implement timeouts.

> can return partial data

Seems reading tar-file from NFS-filesystem may trigger that bug.