Failure to load JSON module, even with workaround provided via instructions

On a Centos 5.8 system, I am unable to follow our instructions (http://www.couchbase.com/develop/php/current) to success.

After setting everything up, I get the following error about JSON:
NOTICE: PHP message: PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib64/php/modules/couchbase.so' - /usr/lib64/php/modules/couchbase.so: undefined symbol: php_json_decode in Unknown on line 0

This is even after I put the json.so as an extension in the PHP.ini file.

php -i shows the proper JSON related output:
~ $ php -i | grep json
json
json support => enabled
json version => 1.2.1

I will note that installing via the new PECL method helps to resolve this, but you still get the error if you don't include json.so in the php.ini file.