Include or require multiple PHP API files

What steps will reproduce the problem?
1. add include() or require_once() statements for more than one .php file in 
google-api-php-client/src/contrib/ along with 
require_once("google-api-php-client/src/Google_Client.php");
2. With only one API php eg. Google_YouTubeService.php my YouTube search works 
fine. Similarly with my Google_PlusService.php Google+ search function, however 
as soon as I put both it the whole function breaks.
3.

What is the expected output? What do you see instead?
I'd like to enter a search term into my form, click submit and have the results 
of a search for that key term in both youtube and google+ be displayed 
together. At the moment I can only get one or the other working. I've diagnosed 
with extensive testing that it's the require() or include() of more than one of 
the API .php files that's breaking it.

What version of the product are you using? On what operating system?
Youtube data API V3.0
Google+ API

Please provide any additional information below.
I'm running my php in a Wordpress template. I don't know if that has any impact 
on this working.

Original issue reported on code.google.com by dev.seot...@gmail.com on 4 Apr 2013 at 3:28

Merged into: #286

User1010 / google-api-php-client

Include or require multiple PHP API files #298