The best solution for this is to upgrade PEAR's Archive package, which the pear installer uses, and after that you won't need to explicitly request uncompressed files when installing new, or upgrading existing, packages.
$ sudo pear upgrade -Z Archive_Tar
You should not have to do this for any other package so long as you do it for Archive_Tar first.
This problem happens because Ubuntu changed the pack/unpack format strings a bit to align them to the Perl behavior, which breaks backwards compatibility. PEAR fixed this in successive versions of Archive_Tar (Ubuntu kept making those changes in each successive version of PHP...). And so the pear installer requires a later version of Archive_Tar than 1.3.11 - details are at https://bugs.launchpad.net/ubuntu/+source/php5/+bug/1434099.
You will need to do this after each 'Software Upgrade' affecting PHP that Ubuntu proffers, as the upgrade rolls back the version of Archive_Tar you have installed locally. It also rolls back the Console_Getopt, XML_Util and PEAR packages.