Long story short, Debian's PHP5 package is no longer enabling JSON support for the widely-used web programming language as the JSON support is viewed as being GPL-incompatible. The PHP JSON code has a line added to its license that simply says, "The Software shall be used for Good, not Evil."
This issue was over "The Software shall be used for Good, not Evil" license clause was originally pointed out last year but is beginning to be a lot more noticeable with Ubuntu 13.10 pulling in the Debian package change.
Debian/Ubuntu users can gain JSON support though by running apt-get install php5-json and after that it works fine (PTS does depend upon PHP5-JSON so this is already a problem I've already dealt with, but this JSON license issue was pointed out in an email today by Phoronix reader "Mark".)
With the PHP developers being unable to find/convince the original JSON code developer to ideally remove this clause from his code, a new JSON extension for PHP is being planned but hasn't been merged yet and there hasn't been a status update in some time.